Some small initial impressions:
I've played through two stages. The first is an action/platforming stage, and the second is more of a standard adventure game - find an item, need to do X to get the item, how do I do that, etc.
The platforming section was pretty standard. You have double jump and lock-on capabilities. Some enemies would spawn at random points. You could lock-on, shoot them, dodge left/right, shoot them again, etc. Usually they drop "Nectarcola," which is just a health replinisher. These are also scattered throughout the level, so I never really felt in much danger of dying. There's some platforming. Did die here and there, but you respawn immediately right next to where you were.
One problem I'll point out with the platforming is that there seems to be a "point of no return" mechanic in play. I.e., if you're on a tall building and you need to get to a platform well below you, you can't just doublejump off the platform and fall down to it. The game will only allow you to fall some distance before it considers you dying from it. Doesn't help that this will ruin your doublejump capability, since you might not have used it yet, but you'll die anyway.
Minor complaint in my book, as I've done a lot of platforming over the years and I can adjust to that easily.
There are tank controls, and like the above issue, it's more of a minor complaint than anything. I mean you get used to it - it's not perfect and I wish there was a better way to handle it, but it's not something to break the game over.
In that stage, I was chasing a perp. You eventually track him down, a bunch of enemies spawn, you take them out and the level is over. Pretty simple.
The "adventure" stage was ok. There are still tank controls (bleh), but you go around and look at stuff, pick up items, etc. The inventory system is a little confusing at first, but again, you adjust.
The voice acting, movies, and music, however, all seem pretty top notch, and easily harken back to the glory days of Lucasarts. There's some nice jazz playing throughout (although you can tell when it repeats, but eh) and the voices are really well done. Sadly, it's not all in voice (as to be expected), so the game portions end up having Animal Crossing-like gibberish voice noises when someone speaks. I imagine the PC version doesn't do this (and I do plan on getting that one as well, I just wanted to support the DS version first).
The graphics are passable - about what you'd expect from the DS churning out 3D polygons.
So right now I'm considering it above average, but I'll play through it some more and give a more detailed account. I'm also going to look at current reviews and see if anyone of them seem out of line, because (as Snake said) this genre tends to get butchered a lot from the editorial crowd.
Edit: Looked at reviews from IGN, Game Informer, and Games Radar. GI's is stupid - barely a paragraph that amounts to little more than "hey I maybe played the game but you can't tell from my abysmal quips about it." GR's is equally bad - they basically sound like they hate adventure games, and were off-put by some of the issues with the platforming, and thus decided the whole thing was a mess. I haven't pixel-hunted yet, but I've played games where you lived and died by such, and even then it wasn't ever an issue that made me want to punch puppies. So I'm guess their review - as it stands - was half-assed at best. Maybe I haven't reached some of the same areas they had trouble with, but the review screams of someone playing a genre they don't know anything about.
IGN's seems the most spot-on for the time being.
Until I run across all these supposed glitches and bugs (haha! pun!) that everyone is crying about, I'm not trusting the reviews.