Guitar Hero & Rockband.
From the outside this looks like a pretty stupid game, slightly above playing air guitar.
Several months ago, a good friend of mine was talking about it one day, and I expressed my opinion about how stupid the game looks. He was going on and on how the game is really fun and he plans on buying Guitar Hero III for the Nintendo Wii next week. So the next time I was over (next week) he wanted to break out the Nintendo Wii and show me the game. He played a few songs and was showed me the song list. Being a rock/metal head there was a few songs I liked (SLAYER!), and so decided to give the “stupid game” a try… well, I was hooked… I called the wife on the way home that day telling her I GOTTA GET ONE and that weekend I picked up the Nintendo Wii and Guitar Hero III. 
I started the game on easy difficulty, but easy is just too easy, medium is kinda easy, and there is a big difficulty gap between medium and hard. I managed to complete an entire “tour” on medium difficulty in about a week. Since then I have completed most of the Tour on hard difficulty, but there is just a few I cant do…
I looked into playing the other “guitar” games while I waited on Guitar Hero World Tour, but it seems the only other game I could play without having instrument compatibility issues is Guitar Hero 2. I could play the Rockband games (Rockband 1 & 2), but I would have to buy new controller(s) since the Guitar Hero controllers were not compatible. My buddy who got me into the game didn’t seem to mind the instrument compatibility issues and purchased Rockband games with new controllers. His living room now looks like a recording studio with 5 guitars & 2 drum sets.
So before buying anymore games, I waited until the latest Guitar Hero and Rockband were out and the instrument compatibility reports started coming in. After reading the reports, it seems that of all the platforms (Playstation 2/3, Wii & Xbox 360) the Microsoft Xbox 360 has the fewest issues. The Xbox 360 instruments (Guitar, Drums, Mic) for Guitar Hero are compatible with all the games; Rockband 1 & 2, Guitar Hero II, III, and Guitar Hero World Tour, and not to mention all the “add-on” packs (Aerosmith, AC/DC, etc). So if your a fan of these games, the Xbox 360 is the way to go. I ended up buying a Xbox 360 with the Guitar Hero World Tour Band Kit. This is the perfect setup, as now I just need to buy the other games (not instruments) to play them.