I'm barely half way through the book, but some of the chapters written in ebonics are atrocious. He starts out the chapter totally over the top and it seems like he forgets he was writing in ebonics by the end. There's just so many places it feels like his editor just said "fuck it".
There are definitely a few sections that I get lost in, but they are so few are far between. I could probably count them on one hand. More than half the book I am pretty neutral about and then there is a significant portion I read and just look up and think, this author is full of shit. I guess its just his style, but when he was describing "eschaton", he has no idea how the game would actually be played. I guess the way it ends up kind of describes that the depths of the game were really beyond those playing it, but thats kind of pattern throughout the book. He has this grand idea and exposition, but it just sort of devolves out of laziness, or style, or I don't know what. I'm kind of terrified I'm going to reach the end of the book and he's going to devolve again and introduce some stupid non-sequiter to wrap things up cleanly, without any introduction or background.
One criticism I hear quite a lot is that DFW's own writing on the topics of addiction and depression are shallow and not representative, though I can't really say how true this is for lack of experience.
The thing that worked for me in I.J. was that Wallace managed to combine elements of comedy and tragedy, not just in alternating parts but often within the same body of text. Some chapters are so tragic as to be darkly comic, in particular some of the descriptions on the backgrounds of members of AA.
Plus, don't forget that Infinite Jest isn't his only work :). I haven't read The Pale King but have heard that it does away with a lot of the verbosity of I.J. and feels a lot more focused, and there are other works of fiction and also his more journalistic essay-ish type pieces, for example those from A Supposedly Fun Thing I'll Never Do Again (the collection, though the titular piece in particular I found very funny).
I'd also highly recommend Oblivion: Stories, even if Infinite Jest didn't gel with you, as I think it's as emotionally powerful but a lot more focused than Infinite Jest. It doesn't attempt the comedy/tragedy mix that I.J. seems to try for, and as a result the stories are shorter but just as affective.