I picked up Marvel Heroes again and have been playing the crap out of it. Got two of my middles up to 60. I love the fact that you get an XP boost for every hero above 30, 50, and 60 (up to 200% with lots of mid/high level heroes). The more, higher level heroes you've got, the better XP boost...so leveling each new hero takes less and less time. More time spent doing fun things in the high levels, where you have a lot more options (both for your character & for content). I've actually got a decent number of max levels, maybe 10, considering I don't play obsessively (unlike my husband who has like 25 60s, not including running Wolverine to 60 3 times (called "prestige levels") (and each time you prestige a character it takes longer to get to 60) to change the color of his name in chat/display).
They recently added a new chapter to the story, and it opens a new patrol zone that has fantastic loot and constant events/boss spawns. And the new story chapter is *hard*...a fantastic change from the faceroll of the previous nine chapters.