IMO it's worth getting. For a DS game, I think it's epic. It has a great depth of content and great graphics.
The use of touch screen for PDA (i.e. start menu) access and several other functions such as dismantling a parked car's security, planting bombs, making molotovs etc. is pretty well implemented, and not as annoying as I thought it would be.
The drug dealing minigame is pretty good if you only got a few minutes to play the game. There are lots and lots of sidemissions to do but most of the rewards are pretty meh, only a few are worth getting.
The storyline I think is a little lacklustre compared to San Andreas and Vice City. I also dunno how this game fare compared to the PSP versions of the GTA franchise.
I haven't finished the game, but I played it for 16 hrs and I'm not that close to halfway through the main storyline.
So yeah, I think it's awesome