There's currently alot going on, and the forums at cryptic are abuzz with people who after playing Open Beta, decided this wasn't the game for them.
The biggest hang ups are, A) It's NOTHING like the Champions Pen and Paper game, B) It's going to have Microtransactions, and C) Zones are instanced.
So why isn't it like the Champions Pen and Paper? Well, quite simply because the reason that the Pen and Paper worked was because of your imagination. Instead in the MMO, you have to use powers and costumes they've designed, and either hope it matches you imagination, or tweak your imagination so that it matches what you get. This leads into the fact that it's also a level based MMO. So you start off as a weak hero and learn more of your abilities as you gain levels (which doesn't match a superhero pen&paper game at all). As for the look of your character, let's remember no MMO is ever truly "done" and they can always add more later. Which I'm guessing is their plan.
What they have now is pretty good, but after awhile you do start feeling limited (I'm saying around the 1000th hero you see you'll start seeing similar heroes). To be fair, I've seen look-a-likes of Jesus, Lincoln, Samus Aran, Superman, Batman, Hulk, Ironman, Goku, Vegita, Spawn, Obi-wan Kenobi, Warhammer Space Marines, a Draenei, various Succubi, and more.
As for powers, the energy builders (auto attack that increases you energy, aka endurance, which you use for bigger attacks) or end-builders, are pretty basic, and they did a good job making alot of them feel different, if even slightly. Each powerset (Electricity, Martial: Claws, Force, Telekinesis, Fire, Might, etc) has it's own flavor and provide some sort of direct damage and aoe attacks. Furthermore they have passive abilities (some are defensive and others are offensive), and you can build your character to act as a tank, dps or support.
The idea of tanking is to get the enemies attacking you, and you want to be able to take a hit. There are "advantages" you can get on some powers that make them generate more threat. Then you have your dps, whose goal is to kill things, and when in that role they do less threat (roles can be switched by bringing up your "builds" screen. Support can be done in two ways, either you're locking down enemies, or you're healing allies (support also has it's own role that can be switched to). These roles provide bonuses to health, damage output, end-building, buff/debuff strengths and more.
The game is more "action" than WoW, in that you can block incoming attacks by using a block button, and it's almost completely necessary to do so to prevent and early death (blocking will change a 200 hit attack to only hit for 80, for example). Aside from that, I didn't notice much of any real difference other than having more attacks that do knockback. The fights are also faster paced than WoW, in that ON level there are some specials that are strong enough to oneshot enemies (archers Sonic Arrow for example). And some attacks use a charge mechanic (in that you hold it down to make it stronger).
The environments have alot of destructability to them, and as your strength goes up, you're able to pick up larger things to throw or bash enemies with. Each stat gives bonuses that are clearly labeled. Strength for example, increases the size of objects you can pick up, improves your change to knock someone down, and helps you break out of tangible holds. There's constitution (health), endurance (energy), dexterity (crit chance and evade change), intellect (pet increase, and better intangible hold escaping), ego (crit damage increaase) and recovery (increased equilibrium and rate of energy building).
Now at times as you level you pick a "superstat" this stat is what your dps increase comes from. So for example you pick Intellect. At that point, Int increases your damage, but you'll still want dex and ego to do crits and bigger crits. You will end up with 2 superstats, so that's something to think about. If you want to tank, you'll likely choose Constitution as a superstat, since you'll be stacking it for survivability it will also increase your damage. This isn't very clear "ingame" and is one of my nitpicks about the game (that it doesn't explain it clearly).
That's how the game plays. You level up, increase your stats and group up to take down evil-doers. Very MMORPG like. There's PVP, but right now it feels like a joke, some players you can't kill even if they stand there and do nothing (since some defensive passives are too powerful right now).
The game plays kinda like Phantasy Star Online, several abilities can be used faster in a sequence, or charged for more effect or damage (sometimes it's better to do 2 shots real quick for 80 damage instead of charging a shot for 100). The world is instanced in that if you go to Canada you'll be in one of 30 Canadas with 100-200 people each. You can switch to another Canada if you want (let's say your friend is in Canada 9 and you're in Canada 18). Zone chatting is for that instance only, but you can whisper your friends on other instances. Grouping let's you guys go together into a zone. This can create some interesting situations. For example, going to city hall, I can go inside, which is it's own zone. I can come from zone 8, you from zone 6, and your friend from zone 18, and we'll all end up in the same City Hall Zone.
Each map has it's edge point, where you can no longer go any further (though at least you can "see" further. This combined with the instancing makes people feel like they're not in a single massive world, and was a reason I've heard repeatedly, as to why people were disappointed with the game.
Finally, there's the microtransactions. This is something we don't really have info on, but just the idea of it was enough to sully the game for some people. When I find out more about what's in the C store, I'll post it.
Bottom line, if you were expecting an emulation of the pen and paper, or want the world to be all together and not sharded across several instances of a map, or if you don't like microtransactions at all, this is not going to be the game for you.
This game is not like WoW, and it might not be what you're looking for. The combat is fun, and the travel powers are great, but the game currently doesn't have fishing.
PS: I STILL haven't found the AH, and I don't know who to ask for it.
PSS: If you don't like superheros, that might be a barrier to entry as well.
PSSS(is that even human?): Thanks for the comment on where the AH is, once I check it out I'll do a post about it.