Rock band is a great multiplayer, and also really fun to play on your own.
I'll start with the single player mode. You can start a "solo career" with any instrument and play it at any difficulty. The first time you play through the solo career, you unlock all of the songs. You also get money when you play through the solo career, which you can use to buy clothes and stuff for your character. I had a lot of fun making my character, and choosing her outfits (which I change often haha), make up, jewellery, and more. i think this is a cool feature, although some people probably won't enjoy it as much as i did. You get more money the better you do on the song. (And also, the farther you get into the solo career, the harder the songs get, and the more money you earn)
In the solo career, you get achievements for beating each difficulty with each instrument, so you have to be really talented at all instruments to get them all.
Each instrument is really fun to play, although my favourite is singing. Guitar is fairly similar to guitar hero, so if you play guitar hero a lot, you'll definitely like it. Drums can be hard to play, and takes a while to get used to, but is still fun nonetheless. And it must be kind of similar to the real thing because my friends who are drum players are usually better than the ones who have never picked up a drum stick before. And, finally, singing. I think the singing is well done, and you do have to be able to match the pitch well to do well. I would have to say there is one problem though. There are some parts in some songs where you tap the mic along with the song to play percussion (usually tambourine or a cowbell of some sort). This can be frustrating and difficult because sometimes the mic doesn't respond very well so you get a lower mark even though you got the beat right. There is a bit of a trick to it, though. Don't tap the mic too hard, and it usually responds better.
The multiplayer mode is fun, too. You can start a band in multiplayer, or just play whatever songs you feel like (and have unlocked).
I haven't tried the online part of rock band, but that also sounds very fun. It sounds like you can play with other people online, which is neat. I look forward to trying it.
Another nice thing about rock band is that you can get new songs online. They might be a bit overpriced, but they're not too bad and you can add songs that you really like to the ones you already have. It's a good thing to have for if you get bored of the songs that come with the game.
Overall, I would have to say this is a great game. I think it's much better than guitar hero because of all of the extra features that guitar hero doesn't have. (Also, people say that guitar is a lot harder on rock band because of the guitar, I would have to say it's not that bad, you just have to get used to the different controller) It is a fun, addictive game that you could easily spend hours playing with your friends. My main problem with the game is that all of the bonus songs are from bands local to where rock band was made. I would prefer to play songs I know. But, other than that, rock band is a great game.