Not without shortcomings, however still a unique and great non-game title.
If you are looking for a typical music game and want to mash out Perfects and get High Scores, then Jam Sessions is not what you are looking for. However, if you think you could find it in yourself to enjoy an innovative and customizable title that allows you to use your DS as a musical instrument, then you might be in luck.
If I had to rate this as a game, I'd have to give it an awful review. The gaming aspects of this title are severely lacking to non-existant. Really, it wouldn't even be worth bothering with if you are looking for a "Game". In fact, even if you buy into the "using your DS as a guitar" aspect of it, don't look for quick and easy short-term gratification here.
However, the free play mode in this title is simply amazing. You can jam out and create some impressive tunes by using your DS as a musical instrument. There are many customization options to choose from, both interface and sound-wise. Plus, even a non-musician like myself can manage to make some nice sounding music. Don't let me mislead you, it can still take a little time and practice, but if you stick with it, I think you'll suprise yourself.
I'm a music lover, but not a musician, and I'm simply having a blast with this title. I want to give this a 9, or maybe even a 10, I really do. I really love this title, but I have to confess that it could have been done a little better. The game-aspects of it should be reworked or tossed out entirely. The chord selection is pretty good, but being able to create your own chords or pick out an individual notes, or slower strums or something would have been nice.
However, despite any shortcomings, I'd highly recommend this to music-lovers, musicians, aspiring musicians, or even the music-curious.