Since I just recently quit City of Heroes\Villains, and to keep myself from going back, I deleted all my characters, I thought I should write up my opinions on the game(s).
First off, I never really enjoyed CoV, as I found 4 of the 5 Archetypes utterly boring. I never got a character above level 16, and the game played liked shit on my old computer so I rarely even bothered with it.
I'll talk about the positive aspects of CoH first:
1. Character Customization
I have never played an MMO with a better character generator than CoH. Hands down, it's the king. I usually ended up fiddling with an alt's looks for longer than I actually played them.
Combat in CoH is rather fast, and is quite easy and fun to get into. Some ATs will be slower than others to solo, but in groups, the combat is usually hectic and a blast.
3. Comic Book setting
The setting for CoH is a nice change of pace from the traditional fantasy settings of so many other MMOs.
4. Superpower graphical and sound effects
Some of the powers have very nice effects and sounds. The mighty "WHUMP" of a Stone Melee attack, combined with the screen shaking makes it that much better. My favourite sound effect is the Radiation Blast power "Proton Volley". It sounds just like the photon torpedoes from the original Star Trek TV show.
5. Story Arcs and Ambushes
The story arc missions are very nice in CoH as they give you more of a background of certain villain groups. It also makes it feel like you're actually doing something heroic, rather than just cleaning a warehouse out of some random thugs. The NPC ambushes usually associated with the Arcs are a nice addition as well. They also add to the heroic feel of the missions.
6. NPC chatter
The NPCs in CoH, whether they be civilians or mobs, tend to talk amongst themselves at times. There are quite a few good sayings, ranging from civilian NPCs talking about your character or someone else's taking down a bunch of villains, to mobs discussing whether they should have "burritos or burgers" for lunch.
Bases are a nice addition to CoH in that they finally give players a private place to congregate and do whatever their supergroup wants. Especially for the roleplayers, it gives them a place to RP without having to worry about people interrupting, eavesdropping, etc.
8. Travel Powers
One of the most fun aspects of CoH, and the biggest difference between it and other MMOs, is the inclusion of Travel Powers. Whether it's Super Speed, Super Jumping, Teleportation or Flight, they all make the game that much closer to a comic book. And with them, it makes traveling to your next mission, etc., that much faster and less hazardous.
9. Sidekicking \ Reverse Sidekicking
This is a great feature in CoH that more traditional MMOs should try and adopt. The ability to play with friends, of differing levels, is a excellent feature. Sadly, this can also be exploited to help Powerlevel.
That's all for the good stuff, now on to the cons of CoH:
1. Repetitive Gameplay
This is the /biggest/ fault with CoH\CoV, and seems like the #1 thing people cite as their reason for quitting. You effectively do the exact same thing over and over again. All that changes when you level up is the villains you face, and the zone you're in. Most missions (instanced) are in a generic map, which are re-used a lot. After you've played the game a long time, you can recognize the map from the entrance.
Combat in CoH is fun, but it's simple and repetitive. And depending on your AT and the powers you pick, it can either be a piece of cake, or tedious as hell.
3. Level Grind
There's a hell of a grind in CoH, especially near the upper levels. I only got to level 38, out of 50, but even there it was brutal. And what's worse, you don't gain new powers each level. Near the upper levels it may be every 3 levels. The reason to level just stops being all that important once you get near 40 (the old level cap), as you can have all your primary and secondary powers by then.
4. Poor Performace \ Lag
CoH must have been written on very unoptimized code, as it runs like shit on most machines. Even my brand new beast of a computer could barely squeak 45 fps out of it in outdoor areas. I can get that in Oblivion, with almost everything turned on. Baffling does not even begin to describe it.
Rubberbanding, disconnects, or just general lag are fairly common, especially when a new patch or Issue is released. Disconnecting in the middle of a mission is very annoying, especially if you're playing solo. The mission map respawns then, so you have to do it all over again.
Some of the ATs in CoH make no sense in a comic book setting at all. Stalkers from CoV for example, have no real examples in comics. They're effectively some bizarre version of a Rogue\Thief from most other fantasy MMOs.
Tankers at first seem like any normal "big, tough guy" from a comic book. The Hulk, Superman, and Colossus are a few that come to mind. But the Tank AT in CoH is like a Warrior in any fantasy MMO. They hold aggro, and can take a beating, that's all. Tanks in comic books are the huge, super-strong guys, that take whole groups of people to take down. Usually they square off against other Tank villains in the comics, as they'd beat the tar out of regular villains.
The villain ATs are the worst, IMO. Most of them are just reverse versions of the hero ATs. Corruptors are reverse Defenders\Blasters. Dominators are reverse Controllers\Blasters. Stalkers are rogue-ish Scrappers. Brutes are reverse Tanks. Only the Mastermind is a new creation. And it's basically a AT that manages it's own mobs. I just found it stupidly easy and eventually got bored with it.
Enhancements are basically items in CoH, as they allow you to boost the effectiveness of your abilities, and they randomly drop off mobs. However, most enhancements that drop are useless to you, or the wrong type, so you just end up selling them anyway. And only the ones from the level 50 raid area aren't available in NPC stores. So there's no reason to trade enhancements at all, as you can just sell them, and use the money to buy the ones you want. I have yet to see anyone selling enhancements. There simply is no player market whatsoever in CoH.
7. Animations \ Sounds
Many of the animations for powers in CoH are sub-par. They either look bizarre, or don't fit the power at all. The accompanying sounds are even worse for the most part. And the fact that all the animations are re-used for Villain ATs, and whenever new powersets come out, you end up seeing the same thing over and over again.
8. Pre-Travel Power game
For some bizarre reason, CoH sends low level characters all over the city, for missions or to talk to their contacts. When they don't have a travel power, not only is this a huge waste of time, but it's also hazardous, as the (usually) higher level mobs can kill them easily. At least when people have Flight or Teleportation, they can take to the skies and be totally safe (unless the TPer falls to the ground). Super Speed and Jumping aren't quite as safe, but at least they're /faster/.
Bases are a nice addition, but for smaller groups the Prestige cost to built and maintain them is astronomical. Plus, if it's a small SG, they'll probably tend to avoid the Base raiding, so a big base isn't even needed. Without base raids, bases add nothing substantial to the game, only minor tweaks that can help out. Almost all of which can be obtained from Contacts around the city.
10. Lack of any Voice Acting
CoH has some cool sound effects, but what confuses me is it's complete lack of any voice overs. Not even simple ones like in WoW when you click on a NPC and they say something like, "Hello there." Those little touches make the game that much more interesting, and realistically, don't add a ton of work to the game's design.
11. Unrealistic Gameworld \ Poor Graphics
CoH is supposed to be in a huge city, yet almost all the buildings are simply squares\rectangles with a texture applied. Everything is very symmetrical, and simple. Yet it still doesn't run well. The characters are not very detailed, and the volume of NPCs\cars is rather low, thus the city doesn't really "feel" like a city.
PvP in CoH is somewhat fun, and more or less well balanced. But it still isn't all that great. Some ATs just cannot compete well in PvP, and others are totally useless. Additionally, there's no real reason to PvP as it takes a longer time to gain any rewards compared to just simply soloing missions. PvP also has no lasting effect whatsoever, just like WoW, so the world never changes because of it. In the new PvP zone with the latest Issue, the zone changes to whoever is winning, but even then, it's not like it's permanent. Nor does it affect anyone outside the zone. So what's the point?
Since I started playing CoH there have been /countless/ nerfs. I can't even recall how the game was when I started, as it's changed so much since then. Some of the major ones were the Regen nerf and Enhancement Diversification. Both of which affected my two main characters. This has become the #2 reason people have left CoH as well. The differences between some ATs\powers in the beginning compared to now is remarkable.
14. No Options aside from Combat
There's nothing you can really do outside of Combat in CoH. There is Salvage for base items, but it's expensive (Prestige) and won't build you much outside of Base Raid items. RP becomes one of the few options, but sadly, the game doesn't even allow you to sit on chairs. You have to move your character on top of one and use a /sit emote, which just looks silly.
As you can see, there are more cons than pros. But it's not simply that. Some of the cons are just that much more defining than the pros. Stuff like, "Repetitive Gameplay".
I tried to keep this somewhat level-headed, and not go off spewing my anger around. But it's sometimes hard to do that, when you've been storing it up for so long.