This is what a rhythm game should be.
The biggest blight is the limited track list, which I will concede is not exactly all encompassing, however once one considers that there will be DLC composing entire albums I'm sure that those will make up for the current lack of tracks.
In essence, The Beatles takes everything good about Rockband 1 and 2 and improves upon it. The game feels smoother and plays cleaner, the hammer-ons and pull offs feel a lot more functional than in the previous installations of the series.
The graphics, while not a necessity to the greatness of a game, are fantastic. I was particularly keen on the Let it Be rooftop concert. It was a nice reminder of the greatness that was the short, forty-minute concert, being so young I have only seen recordings but it is such a wonderful moment in the Beatles' career. The band looked great as 3D avatars, and the music videos and settings they played in were all wonderfully done. My only complaint is that, when you are playing, you aren't watching the videos as much as your music scroll (you should be able to watch while singing, if you don't know the words already then shame on you, haha).
If you like the Beatles then this game will be excellent for you, if you LOVE the Beatles then you probably already own it, and if you just like rhythm games then this may be for you, depending on whether or not you can stomach an entirely Beatles set list.
As much as I love this game and as much as I love the Beatles, I must admit that this game isn't for everyone. If you don't like the Beatles then you will obviously be keeping away, and if you're not sure then it could be a slippery slope.
Whatever the case is, this game is marvelous.