Prime and Other M may as well be from different planets. Totally different, and unrelated in most respects (both gameplay and story). I personally believe the Primes to be FAR superior, but that depends on your gaming tastes (linearity vs exploration, cinematics vs non-exposition, slow and methodical vs fast and arcadey).
Other M has been my least favorite METROID. I don't say this lightly being a Metroid fanatic. But I do say it with experience, as I have just completed it with 100%. It feels more like an Xbox game than a Nintendo game, if that makes sense. Not that I'm bad-mouthing anything, but the feel of the game is very different from the others in the series (other than Fusion). It actually feels very much like a console version of Fusion. The deep mood, music score, and isolation have been replaced with dialogue, cutscenes, and less-realized art direction). For my money, Super Metroid is the best way to spend your dollars if you're looking for 2-D style of Metroid.
