I'm a big fan of the metroid series, and by and large this game made a good transition into 3d. The environments, the morph ball, the overall 'feel' are all very faithful to the series. The visuals are some of the best on the gamecube, and the visor interface completely sets this game apart from other FPS-types.
The issues I had with it though, unfortunately, were enough to keep me from finishing the game -- or even enjoying it as much as it deserved. First off, the control just wasn't there. I figured that I would adapt to it eventually, but I never did. Secondly, the amount of backtracking seemed excessive -- even for a metroid game. Combine this with awkward control, lots of precision jumps and a difficult combat system if you're engaged with more than one enemy and it just wasn't very fun.