From what I've read on the forums, the game doesn't really heat up until you hit level 20. At that point you can start the better missions that tie into the history of Paragon City and you learn all the history of CoH. But even at that point, the missions are all "kill-all-the-bad-guys-and-boss" type missions.
I agree that grinding out levels until you reach 20 is a repetitive pain in the ass. CoH is all about teaming and Super Groups. A lot of people seem to go into it looking for skills, loot, and all that other stuff that fantasy MMORPG's like World of Warcraft or Star Wars Galaxies offer. Unfortunately, City of Heroes is nothing like that.
I don't know that I'll be going back to CoH anytime soon. Not only because I can't pay the $15 a month right now, but I also want the kind of in-depth character progression you can't really get with CoH.