It's inferior to the two preceding Prime games, partly due to its structure but mostly due to a weaker control scheme. In particular the manual aiming makes boss fights unevenly challenging. It's good enough to bother playing, whereas Metroid: Other M is not.
Usque adeone mori miserum est? After all, there's always a continue...
Just gonna hijack this topic real quick to ask my own related question, how much more linear is this compared to the other 2? I used a FAQ to beat Prime 1 & 2 because I didn't like wandering around aimlessly until I coincidentally did something story-related. Would I need to do that in this game too, or would I know exactly what to do and where to go most of the time?
Actually I heard from a buddy that this game is pretty linear. Something about, exploring a planet, fighting the boss, hopping on your ship to another planet. But from what I understand you can't return to previous areas. Buuuut better to get advice from someone who's actually played this ^_^;;
Not really more linear, just more guidance. The ability to fly to and from different planets means there's less backtracking. You can return to previous areas, and it's actually easier to do than in the first two games.
Don't pay attention to the guy who complained about the controls. They take some getting used to if you've never played a FPS on the Wii, but they're far less clunky than in the first two and they make for much more exciting combat.
I'd put this on a par with the first two. It isn't groundbreaking like the first, and the added guidance detracts from the usual Metroid feeling of isolation, but the controls really reinvigorate the gameplay, and it has some of the best environments, boss fights, and puzzles of the whole series.