I love, love this game to bits, but I have two major grips with it: some of the levels, or better yet, some of its level specific mechanics are insufferable.
The Savanah "solar rays" are good idea but they overlap with the yellow shots, making the screen a mess.
And the Abysss... why does the last world has to have the most stupid idea in the whole game? The submarine mines make these levels slowwwww and boring as hell as the whole point of thee game is nullified (shoot at things, avoid being shot) in favour of "shoot with caution and as a pussy." Lame beyond belief.
But aside from that, holy crap, does this game rule. The New York and Paris levels are full of style and awesome, and the shooting mechanic is way better than the regular shump one as it let you shoot from every single position and angle possible without affecting your "spaceship". Another small jewel in the DS library, yes sir.