A modern-set, superhero-themed, fun and rewarding MMO? It is possible. It's not all elves and goblins.
You start off designing your character. This, unlike many MMOs is very detailed, allowing you a lot of choice in classes (called Archetypes here, there's 5 for heroes and 5 for villains) and power-sets (fire powers, super-strength, mind-control, etc) and the seemingly irrelevant choice of origin type. Then it's on to the costume creator. A HUGE part of the game.
In other games, characters change their look as they level up, gaining better armour and weapons and constantly looking different. On one hand, this is good, as it gives players who've gotten to the higher levels something to show off, and less avid players something to strive for, but in COH you can pretty much wear what you like, and it won't affect gameplay. Perfect for superheroes and villains, especially if you're going for a character with a particular theme. Capes are restricted until reaching level 20, and there are a few unlockable costume items but usually there will be something that'd do as a temporary substitute available from scratch. I must say, the knowledge that you can design a character's physical look and not be required to change it every level or so is a hugely appealing factor for me. It helps you bond with the character and invest emotionally as well as establish a presence in the player community.
And what a community it is. On other MMOs I've found teaming both difficult and infuriating. Most (not all, but most) players on the City games are friendly and welcoming of new players and I usually don't have a problem finding a team. And not even for big things, just run-of-the-mill missions. If you want to do a Task Force or other more in-depth, time-consuming mission (and you don't ever have to, they're there but not required to level or anything) then there's usually a number of people willing to lend a hand. Although, by the time you're thinking about these, you'll usually have a few friends who you want to do it with anyway.
People share banter on here, but rarely is it insulting, and I've not often seen people chastised for "not doing their job" right, as there are a number of ways to play the game, and to be honest, any team of 4 or more will usually find themselves capable of completing at least he standard missions with ease. Depending on the difficulty level of the missions, of course, but this can be changed. Nice if you're finding yourself breezing through missions and after a bit more of a challenge. You don't even really need to team up at all. Something I found refreshing after a few difficult tasks on another MMO that were simply impossible without some backup. Teaming is great on this game though, so I'd highly recommend it.
There is PVP, an invention system and an auction house of sorts, but all are simply additions to the main game. I do have one character who has spent as much time inventing and wheeling-dealing as he has fighting, but there's never really a need to. NPCs can buy most pick-ups and if not there's always someone who could use it. Get in a supergroup (the COH equivalent of a guild) and there's usually a storage place for unwanted extras. I'll admit I'm not very PVP oriented so I can't compare that part of the game with others, but I'd imagine it's a bit easier as not every player is concerned only about numbers.
In summary, there's tons to do, loads of variety, plenty of cool people and a setting currently unique to the MMO scene. That's without mentioning the numerous free updates, which recently have been more akin to the type of content other games create full paid expansions for. If you've any interest in superheroes, or even just a fun gaming experience, I'd heartily recommend this over some of the other MMO's out in the World.