Lego Rock Band is definitely the best Lego Rock Band.
First off, the gameplay. The gameplay is your normal, average, hit the notes and get multipliers to score major points. But, there is a big difference that strikes everyone. You play all the instruments. This helps from the cliché that is hitting the notes, and getting points. You use guitar, drums, singing, and bass. You have to hit purple notes, after hitting a series of notes, and then it's recommended you switch instruments, plain and simple. Basically, the gameplay is awesome.
The graphics are your average DS graphics. It's Guitar Hero: On Tour all over again. Unlike the console versions, the band members randomly play their instruments, but, this version is a lot more accurate. Even then though, the graphics aren't bad.
The soundtrack is a lot better than most other music games, featuring songs like "The Final Countdown" and "We Will Rock You". And, unlike Guitar Hero: On Tour, the sound quality is pretty good. Overall, the sound/music is pretty good.
The replay value is decent, thanks to Tour Mode, and the Multiplayer. In Multiplayer mode, you get 3 of your friends, and you all individually play an instrument. The only drawback is that this game doesn't support DS Download Play. Asides from those two, not much else is going for it.
Overall, whether this game deserves a try, or a spot in your collection, depends on whether you like music games. Even then, you definitely should give this game a try.