I'm kinda late to the party (had my xbox360 for about 7months) But yeah I play GH3. Out of the 3 total GH games I have, it [GH3] seems to have the better balanced list of fun songs. Endless Sporadic, My Curse, One, Sonic Youth, Black Magic Woman, 3s and 7s. I just hate when I play a song thats been edited.
It's still my favorite GH game. It's still the only one where I can play multiple dragonforce songs. I play GH3 almost everyday (if I have time to play video games on any given day, GH3 will be one of them). GH3, Van Halen, GH2 and Metallica are the most fun games out of the one's they've released so far (in my opinion). I haven't experienced a whole lot of band play because none of my friends play guitar hero and no one is ever online, but those are the most fun single player games to me.
If your talking about if people play online then yeah GH3 is by far the most active online game of the guitar hero series that I know of. In fact its probably the only one I can even consistently get people to play against except for the odd time on ghwt. Big mistake they made was eliminating a leader-board for online after 3/ Aerosmith which is why I think most people even still play online for 3.
every day i play it. and every time i even think about online matches i find them. I know a lot of people play it because i get 10-15 online matches a day. smash hits i also own i'll be lucky to find one or two online matches. but thats why i friend anyone i play with (who plays at a decent level and isnt a trash talker.) xbox live has people on almost any game at almost any time, just gotta get lucky.