This game is nothing compared to Super Metroid, but SM was one of the greatest 2D adventures of all time, so don't let that stop you from playing it. It's a very solid game that will appeal strongly to those who like the Metroid and Metroidvania games. Note: I've beaten the game and also completed the 4% run.
This game does rip off SM a lot, but it's more interesting for what it does differently. The 2.5D is easily the best I've ever seen. The story presentation added into the game is far stronger because of the ultimately 3D nature of the environments. The game even puts enemies into the backgrounds and lets you fight them. You aim with the right analog stick with complete freedom in 360 degrees. If your laser sight, which normally stays in the left/right plane, crosses an enemy in the background, you aim into the background. It can be a bit disorienting, but it's manageable especially on easy or normal difficulty. I'm extremely interested to see what Nintendo does with Metroid Other M in response to this.
Let's see... what else is different. There is a general stealth aspect to the game. It's not needed in the easier modes, but in insane difficulty, you'd be crazy to just rush into a room and start shooting. Like in an FPS, enemies don't know you're there until they see you. You can get up behind someone and do a stealth/melee kill and then go back into hiding. I really need to replay it on Insane mode... except...
Finally, the game has an unusual system where you gain experience points for various things (killing, exploring and picking up items), but each level grants you a specific bonus of some kind (like increased accuracy or stamina (defense?)) instead of a general increase to all stats. The stranger thing is that once you've beaten the game once, any time you restart a new game after that you retain your experience level. If you wanted to try a fresh level 0 run on insane difficulty, you'd have to start a new gamer profile or else delete your save file from the 360 system menu. That would probably be *really* difficult. Insane mode is probably there to continue challenging people replaying the game with a high level of experience.
All in all, a very cool game and well worth the 15 bucks.