I have been playing a lot of CO, but I'm only just getting close to 20 on my main. I subbed for a couple of months, and my old friend, alt-itis, reared its ugly head. One thing I have discovered in the course of setting up a blog, to document just how much you can get out of the F2P games without spending any money, as long as you give truthful info and a unique email address for each, there is nothing in the ToS for any of the games I've read through so far (CO, DCUO, MH, DDO) that prohibits multiple accounts. I currently have 4 in CO.
I really wish that I liked DCUO. The game play is a little clunky with a keyboard and mouse, but it was designed with a console controller in mind. I have one for PC, somewhere, but I can't find a Windows 7 driver for it. Also, the graphics are amazing, but the machine I play on, for being only a couple of year old, can't handle the settings where I could really enjoy that.
Marvel Heroes is Diablo III in the Marvel Universe. It's really pretty to look at, but I have to have my graphics settings turned
all the way down to be able to play it. I haven't even bothered trying to install and play it on my laptop.
I don't know about anyone else, but I really got into SWTOR, for a while. I haven't been back since my Friday group started playing CO, "to scratch the super hero itch," but it's actually a pretty good game, even for free. There are a good number of people from here, plus the occasional CoH dev. Check the thread in Other Games.