I've been playing for a couple days, and it is really scratching that turn-based tactical combat itch pretty good. If you liked the Gold Box series, XCom, or anything of that ilk, check it out. It uses the d20 rules according to WotC's Open Gaming License, so it plays pretty much like D&D 3.5, except with some minor changes, such as:
- names of some things are changed so as not to refer to any copyrighted D&D stuff (required by the OGL I believe)
- no skills
- only 3 classes (knight (which is really just fighter), cleric, and wizard)
- only 3 races (human, half elf, and mul (half-dwarf I think))
That may sound kind of limited, especially the last 2, but it's not as bad as you might think. Given the plethora of fighter feats, I was able to make 2 very different knight characters (one greatsword specced guy, and one highly dextrous 2-weapon fighting guy). But the detail in the implementation of all the various combat rules, such as grappling, blind-fighting, concealment, etc pretty much overshadows any of the perceived downsides, I find. The AI is pretty hardcore, too, they will pound on your wizard mercilessly and react to your spell choices with good counters, etc.
Also, the art is decidedly old-school, as in low-res. The font up until today's patch (1.10) was an almost exact clone of the old Gold Box font (which may or may not cause you to shudder), jaggies and all, but now the font has been smoothed and is pretty crisp and readable.
The game makes extensive use of in-game hotlinked help entries that explain just about everything in the game (like what different modifiers mean, what is causing them, what conditions are affecting a character, what feats an enemy has, etc), that is pretty nifty.
Anyway, there's a demo if you think it might be your cup of tea. The full game is about $25, and is purported to be about as long as Baldur's Gate (I couldn't say, I'm only about 10 hours in / level 10 party).