I heartily recommend Echoes. Nick's on the fence about it, but I like it for what it is. Echoes is more about exploration than Prime, which is more goal-driven. It's got a slower pace and it's a tougher game, but it's different, which I ultimately like, and the suit designs are cool.
Lessee...last night I nabbed the Ice Beam and started through the Frigate before realizing I needed the Gravity Suit. Oh, getting back UP the flooded room is SO FRUSTRATING. But I got a TON of pickups, and my logbook is already 64% complete. I was sure to nab the one scan I always forgot to grab on the GC (Ice Shriekbats). I haven't noticed any NA/PAL differences yet, but now I'm looking for them.
I'm going out of my way to nab as many pickups as possible whenever I get new equipment. I cuts down on total gameplay time and makes fights easier overall. After playing through Zero Mission, Fusion, and Super Metroid (all recently), I'm finding myself using Missiles a lot more than I used to. Once you're locked onto something, a missile is often more accurate than your own aiming, though I still use the one-two punch of charged Ice Beam + missile.
God, I love this game.