i have a blast playing UC2 MP. I agree it does take entirely too long to level up. I'm an average player and it will probably take a week or two for me to get from level 49 to 50. Maybe I need to get my skill up but I'm lucky if i get $10K in a match.
The last shooter I played was the first Half Life game so I can't compare it to MW2 or any of the other games, but I suspect the platforming and climbing aspect of UC2 puts it somewhat in a league of its own.
Late join is needed. I hate having to battle it out 3 vs 5 and getting my K/D ratio destroyed. It happens entirely too often
Online isn't dying - it's growing. Seen TONS of low-level players in the post-christmas weeks.
Only major changes they need to make are a way to kick idling players, a way to deal with people who play Plunder like a deathmatch and never attempt to score, and a way to see player names instead of just "Player Found" so you can avoid games with people who you don't want to play against.