Here is my impression after playing it for a week (made 5 or so chars and played them all to lvl 12-13). The game obviously still is very new so I expect it to get better later on, and alot less annoying (2x maintenance a day, etc), but at the end of the day the resemblance to any other MMO filled with carebears, faggotry and lots of retarded stuff that makes me rage is uncanny.
That said, let's get started.


General Feel:
Champions Online suffers from the same problem EVE has in my opinion- a single server with many different instances. One should think one server would bring players closer together, but that's not the case. What it does do is causing people to killsteal each other like mad. What it also does is making it feel like you're playing a singleplayer game (apart from the few people that don't understand that /zone != /pm) because you don't often see other players (and when you do they rather steal your mobs than team up).

Which leads to the next problem: the game doesnt have a good grouping system (yet?). In WAR/WoW/whatever you can list yourself as looking for a group and people can invite you, join your group through the interface and so on. In champions online you have to ask in /zone if there is anyone who needs the same mission, if there is noone responding you gotta switch to another instance of the same zone and repeat.


Combat:
PvE is meh, some builds are plain shit because they seemingly didnt properly balance powers yet so you might find you can easily dispatch 5 mobs at once with one character, not with the other (and I'm not talking "tank build > support build" but "Ice build > Fire build" for example). There are mobs everywhere in the zones, if you have to quickly go afk you better have a flying power or be prepared to find your character dead when you get back. The fact that most mobs come in pairs of three doesn't help this either.

PvP is...well, not very fun.
Mainly because of travel powers and (less so) crowd control. The travel powers allow people to just teleport out of reach when they get low on HP and heal up which is absolute ass (you'd need to be ready to root [or "hold" as they call it ] them when they get low to try to prevent this). Which introduces "holds", abilities that root you in place and often prevent you from using any skills until you break out of the hold by frantically spamming Z (assuming you're still alive at that point).
Especially the holds make clear why "classless" MMO's aren't very popular: you end up with some abilities everyone uses, that don't have a direct counter (a dispell for holds) or are just broken/stupid (teleport).
Talking about stupid, there also is Regeneration. It regenerates a base amount, and more if you recently took damage. What that effectively means is that you have to outdamage the other guy's regeneration- that's real fun..
I'm being told that CO is PvE focused so I doubt they'll ever get PvP right (replace "right" with "less shit" imo).
The lag doesnt help combat either, with lots of abilities being charge-able you end up just tapping a power rather than charging it because the onscreen charge-bar of course doesnt factor in lag; there's only so many times you can waste an ability on a 20 sec cooldown before it starts pissing you off.

One big plus for the combat in CO is blocking. You have to actively press a key (shift by default) to block, reducing incoming damage (massively), even neglecting some CC effects afaik. Great mechanic and should prevent too much facerolling in PvP.

The last point of this section better fits into the next category, which is...


Maps:
For PvP there seemingly only is one map for tiers 1+2 (lvl 1-20) which is a caged arena.
It's allright but after a few rounds you've had enough of it.
I know there are more PvP arenas later on but they should really add more variety for lower tiers, afterall who wants to keep playing the same old shit for weeks just because there's "more later on".

Back to PvE, after the tutorial (which is nice, for the first 1-2 times you play it, after that you wish you could just skip it...which they're working on apparently) there are 2 areas you can go to. Either, not both- you'll have to make a choice, allthough at lvl 12-13 you get to go to the other area. They (canada and desert) are allright but it takes more to impress me when it comes to PvE...

After desert & canada you finally get to go to Millennium City which seems surprisingly dull so far. I couldn't possibly say more about it atm though so I'll leave it at that.


Misc:
They stole the "public quest" mechanic from WAR, meaning you enter an area where a public quest is going on (defend objective X, kill X amount of Y, and so on) and you and everyone who was helping with the quest gets some XP and items when the quest is done (supposedly based on contribution, doesn't seem to factor in heals though which is fail). The mechanic is fantastic, but unlike WAR they're sparse. I think there's around 2 PQ's on each map...PQ's are a great way to find decent people to run normal quests with, just find people to talk to that aren't drooling morons and...well, they're actually fun. I guess they figured the low amount of PQ's would go well with the whole theme they got going there, discouraging human interaction.

The normal quests are okay, some of them are actually quite challenging.
Escorts quests, gather quests, reverse-gather quests (find wounded soldier and heal him using this item etc), kill quests...nothing out of the ordinary technically.
I say technically because you might actually get jumped by 10 mobs at the same time while you don't expect it during a quest; it's small variations and challenges like that that make the quests in this game less horrible than in other MMO's.

Don't think I need to say anything about character creation, it's the best part of the game. If not for that I'd probably regret buying the game. Also, you're allowed to have spaces, full stops, etc in your name which is nice for a change. One of my chars is called "The Decioblidevannihilator" so you can tell the character limit is almost non-existant.

Loot...your character has 9 equipment slots, 3 for each offensive, defensive, and utility items, the items you gain go into those slots and...that's it. Doesn't sound impressive? It's not.
At the developer chat yesterday one said they're working on item-sets which I suppose is the best one can make out of a system like that.

Crafting is alot like loot/equipment, useful but not very impressive.

The UI, HUD and controls are fairly customizeable, nothing mind-blowing but above average. No complaints from me.

As a last point I'd like to talk about the make-believe classlessness in CO.
With time they'll add more content and you don't have to believe that you can get by without a healer/support and a tank in a group-instance. Just saying...it's gonna be like most MMO's, you'll have a few might builds capable of tanking and a few support builds with decent heals/buffs and about 80% DPS builds that are good for...nothing (in PvE, of course). It's bound to happen that way, unless they add even more powers that regenerate your health, at which point you might as well not group at all since you can do everything yourself...right?
Individual chars are more powerful but you'll still need the above mentioned pillars to build a foundation.


My verdict (a.k.a. tldr):
5/5 atm, can go either way depending on future developments in the coming weeks and months. I'd say it's a good game if you want to play it casually for an hour or two after work or while your main MMO is on maintenance but for a "hardcore" player CO is lacking too much at this time. if you think about getting it, wait a few months imo.