There still isn't much variety in gameplay, it's always fighting something. However, the gameplay changes drastically post level 20 (you start fighting different groups of mobs with more powerful powers), post 30, and post 40. Eventually you start fighting mobs that can kill blasters/defenders/controlelrs in 1 shot, so effective grouping becomes much more important.
I enjoyed Task Forces, which are 2-hour + missions that you must start and end with one group (no one else may enter the group). It adds a nice dimension where you actually are forced to get to know group members.
They added badge-collecting, which is kind of a fluff addition. You get badges for killing different kinds of mobs, exploring areas, dying a lot, healing a lot, being stunned a lot. I never really got into collecting, but a lot of people did.
I was a real fan of the gameplay after level 20, when the game gets a lot crazier and difficult. It's very fast paced and you need to pay attention, which is why I'm such a fan of the game. It does get repetitive until then, especially if you don't have a travel power, and the groups of mobs are "blah." But after 20, you really start putting the "super" in superhero.