i've had rock band for like six months, i've played it quite a bit. i played it a bunch this afternoon and i've been coming to the realization that i don't really enjoy it that much. i will definitely say that the amount of fun is directly proportional to the number of people playing (the game is not fun in single player mode), but these are my issues with it:
a) the rock band equiment that it comes with is garbage, but i'm sure basically all the reviews have said that. poorly made and the stuff breaks easily and frequently.
b) i don't like the layout of the drum set. not that i'm great at drums, but i feel like i could do better if my arms and the other pads weren't necessarily in the way at times. it doesn't feel 'natural' and everything is kind of crammed together.
c) the drums are really fucking loud. if you're going to play and hear over the drums, you have to crank the volume.
d) i don't like the difficulty level. i have played GH games quite a bit and they are harder. i don't have a problem with RB being easier, but it gets to the point where the songs are mind-numbingly boring (not just because of the notes to be hit, but some of the song choices are really questionable and they just suck, IMO. i don't mind playing songs i dont like i they're fun to play in the game). even on hard/expert, a lot of the stuff is really easy, but then all the sudden you hit one of the one or two songs that are just ridiculously hard. i don't know if it's just that my style of playing isn't suited to some songs, etc.
e) i don't like that you have no choice but to play the same songs over and over and over again. it seems like no matter what, when the songs are randomly picked for you (either from a random setlist or the ones that pop up that you're forced to play as individual songs), you end up playing the same tired songs (in bloom, that garbage song, that ok go song, etc) over and over and over again.
i have higher hopes for GH4, but i hope that they don't make it "artificially difficult" like they did GH3, where the arbitrarily added in extra notes to be played just to make songs harder. i'm most of the way through both hard and expert in GH3, but there are songs i just can't beat.... like raining blood. my fingers just do not do what the game requires me to do to pass certain parts. i think it's a bit ridiculous to go from being able to relatively easily 5star the song on medium to failing like 30% in on hard when you've already beaten every other song on hard mode (without too much of a problem).
the drum set for GH4 looks a bit nicer (and sturdier) from what i've seen, but i still don't 100% like the way it's set up.. but i suck at drums anyway, so i'm sure i'll just be doing guitar/bass anyway.
the DLC is nice for rock band, but i feel like the stuff is coming out pretty slowly and it's relatively limited, though i have to say i am interested in playing some songs from dolittle when i get around to downloading them.
DLC for gh3 was absolute shit.