[Disclaimer: Since there is no difference in gameplay or options from the original Rock Band game, this isn't a full fledged review]
In December and June, Rock Band came out for the PlayStation 2 and the Wii in that order, both after the Xbox 360 and PlayStation 3 versions. Although they came out after the other versions, they both lacked more features, including online play, Create-a-character mode, and of course, DLC (Downloadable Content). Now, Harmonix has fixed the problem by releasing track packs, which are just like the original games, exept the track packs contain only 20 songs, all different.
All the modes that the Wii and PS2 versions have are included in it: Solo Tour, Band World Tour, Tug of War, Score Duel, and everything inbetween. Unfortunatly, they still don't include online play, another big thing missing for a delay in release. What is also bad is that it contains 20 random tracks, or in other words, tracks of their choice, not yours. Don't like Boston? Too bad, it's in there. Like Meticalla? Nope, not in there. So you may only discover a few tracks that you like, but you would still have to buy the whole $30 price tag just to play the few that you like.
One thing to be sure of, you should buy the actual Rock Band game, which includes 58 tracks (63 on the Wii) for the cheaper price of around $50. When you do all of the conversions of Xbox Live points, you'll find 20 tracks on Live is a little more money, but paying $30 for tracks you just don't really like is not acceptable from Harmonix. An easy tip is to just wait until the 2nd Track Pack comes out.