Stellaris End-All

Gameplay & Ship Editor
Like Crusader Kings 2 or Europa Universalis 4 Stellaris runs in pausable/accelerable real time.
At the start of a game we tinker our own race via a populace editor. We can choose bonuses and penalties like production or research bonus or traits like"xenophobic", "religious" or pacifistic" which determine the further course of the game considerably. Then we choose one of 100 portraits and with it the appearance of our people - and there you go!
While there are also prefabricated races they are only intended for quick start - for people who don't want to edit. In the game itself you will not meet these races.
After all, the properties of all adversaries are completely randomly generated in every game! So you never know in advance if you'll meet fanatically religious squid researchers, xenophobic mushroom creatures or isolationist cyborgs in the vastness of space. While this could limit the uniqueness of the races it can increase the replayability. There should be thousands of combinations of the diverse traits.
The galaxies of Stellaris are randomly generated from a chosen size. At the presenation the developers zoomed seamless from individual suns and planets up to the whole galaxy. Which looks big. Bloody big.
Each of the up to 16 adjustable enemy races starts with only one planet and must expand. In addition to these 16 "upstarts" are other inhabitants of the galaxy in different stages of development. More about that in "Phase 1: Exploration".
Spaceships move freely through space and not on predetermined paths. In order to safeguard important flight corridors, one can build starbases or lay minefields.
Battles between fleets take place directly in the game view, there are no separate tactical maps. You can't control the battles yourself, they run automatically - just like Europa Universalis or Crusader Kings.
There will be an editor in which we equip our ships with weapons, reactors, engines, etc and thus can design our own models.
Obsolete Ships can be upgraded at home to the current state of the art, but this takes some time and costs money.

Colonies & Heroes
Each colonized Planet offers several grounds slots on which we can build one building each. Several similar buildings (for example factories) side by side enjoy synergy bonuses and produce more.
The tiles have different properties with advantages and disadvantages. Alien Ruins for example increase the research output; food farms should be on fertile fields rather than in ice deserts. And areas that are inhabited by dangerous animals must be purged first - which in turn requires the appropriate technology. Thus the planets are likely to greatly stand out from each other, a desert world will never be the food basket of the empire.
In order for a tile to produce something we need to assign workers on it. Per population point we have a "workers unit" available. But beware: Just like a roleplaying character each population unit has individual qualities that Stellaris generates based on the initially selected national characteristics - for example "industrious" (good!) or "xenophobic" (bad if other races live on the planet) .
RPG-like characters play an important role, as in Master of Orion special heroes are available in Stellaris. Namely leaders (lead colonies), admirals (command fleets), generals (commanding ground forces) and scientists (fly research vessels, more on that later).
Each character has certain advantages and disadvantages and levels up by successes. Thus you should distribute your subordinates wisely. This reminds pleasantly to the often illustrious princes, bishops, etc from Crusader Kings 2.

Phase 1: Exploration & nonlinear research
In the first phase of the game you explore the universe with research vessels on which you assign a scientist as a commander. They then naturally bring individual abilities (and maybe disadvantages) with them.
The research vessels can, among other things, scan planets to find out their properties.
In the vastness of space the research vessels can make special discoveries which lead to various follow-up tasks. For example one finds an asteroid on which a temple stands, which is oddly enough dedicated to an ancient human deity. Now one should find out what it's all about.
Depending on the characteristics of their own people and the scientist involved you can choose different decisions. Religious researchers could simply blow up the asteroid as blasphemous and experience a completely different sequence of events than non-religious scientists who could search for more shrines and unravel the mysteries behind it.
Each event can succeed but also end in disaster. When an incompetent researchers examines the aforementioned asteroid there is a risk that the boulders leaves its orbit and is on a collision course with an inhabited world. Then our fleet needs to intercept it.
A quest log (called"Situation Log") lists our open events.
The asteroid is just one example of many. Paradox promises varied events. In addition there are your usual monsters waiting in space like interstellar giant jellyfish.
The regular research extends nonlinearly in Stellaris, there is no fixed research tree!
How does it work? First of all we have the three areas of research for which each a scientist-hero is responsible. The three areas are "Physics", "Engineering" and "Society". At certain intervals these researchers make new discoveries from which we have to choose one out of 3 technologies. For example improved laser cannons, shields or ground forces weapons.
The highlight: the discovered technologies are not predetermined but are drawn randomly from a pool. Here Stellaris also uses the character level and the characteristics of the researcher employed, our national characteristics and the previously selected technologies.
If we, for example, use an experienced laser scientist and have previously developed energy weapons, the chance increases to research high-tech blasters. A "mad scientist" however, produces more experimental technologies. The system should help the individualization of our race and at the same time ensure that the progress feels natural so we don't discover Death-Star technology at the start of the game.

Phase 2: Conflict & Contact
Eventually in the course of the game we meet one of up to 16 rivals. The diplomacy system is similar to Europa Universalis 4: We can build alliances and non-aggression pacts, make trade deals and even make inferior nations our vassals.
If you get along particularly well with one or more neighbors you can even set up a federation à la Star Trek, an alliance of semi-sovereign members comparable to the European Union. With the difference that a leader of a member nation rules this Federation as president and therefore determines its foreign policy. Every few years there are elections in which a new president gets elected. Depending on the characteristics of each nation the Federation as a whole will act differently: If pacifists come to power, diplomacy is in the foreground; if an aggressive faction wins the race, expansion is announced.
To start a war in Stellaris we should also have a reason for war (casus belli). For example by falsifying the claim of our people on a solar system. Without official reason for war our reputation suffers and we'll soon see a powerful enemy alliance against us. However this can also happen if we expand too quickly.
Wars are not simply just won or lost, instead there is a "War Score" ie. a points value which indicates how much the enemy would give us in a peace treaty. For example we can demand nothing or just some money, annex whole solar systems or even completely vassalize small states and make them our puppets.
In the galaxy of Stellaris we not only meet starfaring races, but also those which may be scientifically advanced but can't reach into space yet (Poland for example). How we deal with these neutral planets depends on the properties of our people. Pacifists can watch them from hiding to collect research points. More radical scientists can abduct people and subject them to studies; warlike races just conquer the planet. And of course we can give the residents the spaceflight technology to include them as a member of the galactic community. Or add them in our own federation, of course completely altruistic.
Apart from such advanced races some planets are also inhabited by races that have not yet developed self awareness. As a ruthless ruler we can intervene in the evolution of these aliens to tailor us a slave race of our own design. If our own people have problems with surviving on a desert planet - no problem then we simply tinker our own Fremen (Dune, of course). And if we have weak troops we just breed us a race of willing soldiers - the Jem'Hadar from Star Trek: Deep Space Nine send greetings.
And there is a third type of neutral nations: the fallen empires. This great star empires had once powerful technologies but lost all their knowledge - just as the human Imperium of Warhammer 40K. They can still use their high-tech ships and weapons still operating but can no longer repair or rebuild. The fallen empires therefore don't expand and start any wars, but doggedly defend their borders - with very advanced fleets. Whoever attacks them must reckon with hard resistance but also has the chance to get particularly valuable technologies that can't be gained otherwise.
Destroyed fleets leave behind debris which can be studied by research vessels to extract technologies. Anyone who has always envied their neighbors because of their bigger laser cannons can therefore easily steal them. Assuming he defeats one of its fleets.

Phase 3: Endgame & major disasters
Typically the endgame of a space strategy game always develops the same: At some point you're so big and powerful that you simply wipe away the remaining competitors. Stellaris wants to do it differently. When your empire grows it also increases the risk of a galactic catastrophes that makes the endgame particularly demanding.
There are several types of galactic disasters that are always based on the current state of the game itself. For example when somebody intensively researches about wormhole technology it may happen that a portal opens into another dimension inviting as powerful as evil aliens in our universe.
Another example: When we have discovered the appropriate technology we can build robot-workers for our colonies who toil very effective and are never unhappy. Anyone who has seen Battlestar Galactica knows: This can backfire! The robot can in fact develop awareness and establish their own machine state. And eventually decide to extinguish the meat bags that contaminate the rest of the galaxy.
If such a disaster occurs we have two choices. Either we unite all the races of the galaxy and fight the enemies together. Or we lean back, strengthen our fleet and wait while our competitors fight - only to all intervene at the end and mop up what remains.