Aside from the perspective, this is true GTA fun.
Long story, lots of fun ways to make money, a few new game mechanics, adult themes and language.
The Bad:
A few missions are, as usual for GTA, extremely frustrating. Driving fast can be difficult at times.
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No, the developers did not pay off the reviewers. It really is as good as everyone is saying.
The stills do not do the graphics justice: this is a big interactive city with lots to do, lots of missions to tackle, and many cars to drive. The taxi, ambulance, firetruck and police car missions are still here, the town is laid out as you remember it, there are many drug dealers to make money buying and selling drugs with...it has it all.
The perspective is turning purists off, who feel that it is reversing direction back to GBA days, which is false. The perspective is NOT top down, it's more of an over the shoulder from far away. There is still a great deal of detail in the world, and you do have some control over the camera placement, and once you get into it, the game becomes GTA through and through.
I admit, I got fed up with the PSP iterations of GTA, mostly due to the later missions requiring many many repeated attempts, requiring a great deal of waiting around for them to load. This is not an issue here, as the entire city seems at your fingertips in a flash. I see games like Galactrix, that require a load screen every time you blink, and wonder whether they purposely included delay screens to increase the game life; GTA never requires you wait more than a second to see the next cutscene, and going from the game to your inventory to the game again is virtually instantaneous.
In short, believe the hype. This is well worth adding to your library of DS titles, if only for the fact that it is aimed squarely at a more mature audience, a testament to the fact that there are some of us who do NOT want to play My Little Pony.