RB peripherals on Wii NOT compatible with GH games.
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I've gotta echo Afx on this one, as someone in pretty much the same situation as he. The GH drums are so good. There were a lot of complaints regarding reliability but mine haven't been too bad. Wire came loose on one pad but soldered that back on myself (i have nearly no idea about electonics) and worked fine ever since. One thing I know is that the GH drums are far better than the RB drums. And if you can get a hold of the new style GH drums (might only be available on US import at the moment - not sure) then do it.
I sang the praises of GH for such a long time, like Afx owning all the games and pretty much being able to compete on all levels of difficulty for all instruments. However, recently got RB2 and suddenly I realised what I'd been missing since GH3 (GH3 is my fave of all GH games but alas, it's only for guitar-no drums/mic). RB2 is brilliant and IMO much better than GH:WT and GH5. It's much more fun to play. That doesn't mean GH is bad. I prefer the drum tracks on GH but prefer the guitar on RB.
Also, whilst there's alot of DLC available for both, I think the RB DLC is much more appealing. GH DLC seems mostly about stuff that the USA teens like. RB tends to cater for a wider audience and I think acnkoweldges that the rest of the world also buys this game, not just north americans.
Oh but don't take Afx too seriously though, he's from the dark side... WAIT, SO ARE YOU!