Near endless fun with this title; held off for months to buy this because I didn't want the extra clutter and noise of the drum kit, but finally broke down and when it was delivered, spent about 8 hours straight playing with all the different options.
The addition of the vocal tracks, drums and group play make this many times more enjoyable than GH, assuming you play as a group, are interested in the drums or singing.
The drums are definitely the most difficult track for anyone who hasn't already played. As for the comparisons between real drums and the RB controller kit, a decent complete drum kit costs "just a bit" more than the $80 RB kit when bought separately. And you can learn the actual drum sequences for songs and pick up a real sense of rhythm by playing the game all the way through Expert, not that it would necessarily make you a good drummer on a set of real drums. No real notes with RB drums.
But you'd still be a LOT better than someone who mastered Guitar Hero and then tried to learn how to play a real guitar.
Once you're past that real drum starter kit, you'll end up paying the same amount just for a set of cymbals or a single snare drum, so it's not much of a comparison in dollars for entertainment value unless you're serious about learning to play the drums publicly with a band.
This drum analogy is kind of like saying, why learn to master Call of Duty 4 when you could buy a real AR-15, go to the range and learn to shoot for real.
BTW, there is a game being made that will teach people how to play a real electric guitar with a Guitar Hero/Rock Band like interface. Guitar Rising. It won't see the same popularity as RB or GH since it requires the purchase of a real guitar and considerably more effort than a 5 button, one strum bar controller, but for those actually interested in playing for real, this game should be phenomenal.
http://www.guitarrising.com/