I've noticed that Rock Band 2 has some type of delay in it. Like, the audio and video is in sync, but when I strum, it registers it like 0.4 seconds late, so I can't stand playing Rock Band 2 half the time. I can blast through super hard songs on GHIII on Expert all day, but put me on Expert on RB2, and it just doesn't happen. Slowing down the game in practice magnifies the strum lag issue. (Try it with Master Exploder on 50% speed and pay attention to when you strum vs. what's happening on the game)
However, on to your question Shadowbrain, Rock Band games' (especially RB2) have a slick and awesome presentation/gameplay as an added reason of why it's better than Guitar Hero. Song selection is pretty good, instrument quality is not better guitar/bass-wise. I can't stand the RB setup. I much prefer precision clickiness and relatively clicky buttons. Other than that.... hmm, dunno.
I like both of the series.