Nolan! Spoilers! Don't read this!
Heh, there's no THAC0. It's very much d20, but they've removed a lot of complexity. Some quick summaries: no more Fortitude, Willpower and Reflex saves (instead, there's a saving throw for each ability), no more endless modifiers to a d20 roll (instead, you can be advantaged or disadvantaged: roll 2d20 and choose the highest or lowest result), no more Skills (they're in there, but they aren't actually named as Skills, just as Common Tasks). Vancian magic is back. Fighters are "boring" again (i.e., there are no named powers for them - it's back to the player describing the awesomeness he'd like to do, instead of a game mechanic). Minions are gone (at least, based on the included adventure).