I've read Infinite Jest. (Actually, that's one of the relatively rare books in my collection--a first-state, first-edition hardcover with William T. Vollmann's name misspelled on the jacket).
I found him to write like Thomas Pynchon, except without Pynchon's ability to structure an extended narrative. (I won't spoil the ending of Infinite Jest, except to say that it steals from a high-modernist novel I won't name, and that I thought the way he wrapped it was bogus.)
Another reason I prefer Pynchon is that Wallace seems to be bending over backwards to impress you with his intelligence, while Pynchon, who's more in command of his material and just plain knows more, seems to wear his knowledge on his sleeve--there's something kind of offhanded and humorous about the way he throws information at you. It's hard to describe in a quick post--the best way is to say that I feel pretentious when I read Wallace, but not when I read Pynchon (who's a more challenging writer to deal with in his long books).
I wouldn't say I hate Wallace like enjoy bell woods does (though I do hate Mark Danielewski's House of Leaves, another popular pomo book with footnotes and whatnot, that got a lot of academic attention despite the fact that it was about as deep as Matrix Reloaded). But given the choice between reading a new DFW novel like Infinite Jest, or reading Pynchon's Gravity's Rainbow for a fifth time or William Gaddis's The Recognitions for a fourth, I'd take Pynchon or Gaddis over DFW.
