I've been putting some time into this one lately, and it's been pretty good so far.
Of course, the writing is shitty and the VA painful, but I don't really care. I also find the upgrade "system" (apart from the logic behind the power bomb) to be really, really stupid.
Oh well, it looks and plays good: fast and fluid. It's definitely a change from the slow, methodical pace of the Prime series, but it loses some of the atmosphere in the process. Probably my one major complaint is the lack of the superb atmospheric soundtrack. Right now, it's just, there.
Although the Metroid series is one on my favourites, I can appreciate a different perspective on it. Something about the battle system, with the sensemoves and lethal strikes is incredibly satisfying, even if it is somewhat out-of-place. I wouldn't want another game in this style, but I'm greatly enjoying it at the moment.