Yo doods, I got this game. I can't for the life of me figure out why it's only averaging like 60% in the reviews. Actually, here's a hint: the Gameboy version got 80% from IGN. I think basically everyone's penalizing it for being a Game Boy to DS port. The thing is, it's still a good game (well, so far).
It's not a Metroid clone. The plot is definitely a tribute to Metroid (there's a location called Brin Talon) but the gameplay is more like a cross between Metroid and Solstice/Equinox. You move run in eight directions around isometric maps shooting everything in sight. So far I've picked up a cool grappling hook that lets me drag stuff around (including monsters). Finding save points is the main similarity to Metroid, and it's even more important here because they also decontaminate you - without decontamination your shields eventually fail and you start to die due to the Scurge virus.
A major complaint is that the game is basically a GBA to DS port. A slightly interactive map appears on the touch screen, it's definitely not an amazing use of the screen, but this game benefits from a map. In fact its's just as relevant as most of the stuff on the touch screen in New Super Mario Bros. The graphics and sound are definitely below average for DS, but they don't change the fact that it's a good game.
There may still be real problems with the game, I've only played for an hour. Always having to reach a decontamination unit may become a pain, or maybe the gameplay will become too repetitive. IGN argued that the GBA version is just as good and probably cheaper...I'll buy that, but at the same time I couldn't find the GBA version anywhere and this was only $29.99 Canadian, which is $10 less than the average DS game and pretty good even by GBA standards.