It's the same old story when discussing Metroid Prime 2 - either you thought the dark world was bland and tedious or you didn't, and that determines where you put the game in the trilogy. Judging from this thread, it's a roughly 50/50 split.
Unfortunately, I'm firmly in the 'bland and tedious' camp. What I love about Metroid is the exploration. Every new room is some gorgeous architecture full of interesting stuff to see. In MP2, almost half the rooms are just clones of stuff you've already seen, but painted a bland purple. I didn't enjoy that.
Not only that, but the dark world falls between two stools. Had it been actually dark (as in, a lack of light) and super-dangerous, then short spells in there could have been tense and fun. But it's not dark, and it's only dangerous in the very start of the game. Once you get the Dark Suit any fear of the place is gone forever.
On the other hand, had it been another interesting interconnected world to explore that could have been amazing too. But it's not, it's small areas of rooms that are dull purple versions of the main map with very little interesting to see and that aren't really interconnected.
I must also be that one guy who doesn't entirely love Sanctuary Fortress. It bleeds into my other problem with MP2 - the setting / story. We're told that the Ing have overrun this world, that there was this huge war (which we see no real evidence of). The Ing also look a certain way, visually. But then you get to their base and there are essentially none of the buggers there and these black slimy monsters live in... a Tron set?!? I couldn't buy it as real, I really couldn't. It was a magnificent level, eye-meltingly gorgeous, but it was a 'level', not a real place.
On the other hand, I loved the hub world, Agon Wastes and Torvus Bog. Loved the light world parts of those places. The highs of MP2 are actually higher than MP1, and the boss fights are far, far better.
It's still a magnificent game, a 9.5/10 at least. But MP1->MP3->MP2.
