For people sitting on the fence about getting the game, I thought I would comment on some of the nuts and bolts.
In General:
One of the best places to learn about an MMO is while playing other MMOs, since discussion of competing MMOs come up frequently. While playing WoW, there were of course the flame wars about WAR, plenty of people talking about how they used to play EQ2--now EVE hardly ever came up but let's face it there can't be much overlap--but City of Heroes (and Villians) did keep coming up and whenever it did, people would reflect on it positively. Although I'm more into fantasy than comic books (and more into Sci-fi than either), I've heard enough good things about CoH to capture my interest. Bottom line, Cryptic has good MMO experience under it's belt.
Character Creation:
I love creating characters. I've deleted level 20 WoW characters and started over just because their hair was slightly the wrong tint. When it comes to getting your vision of a character into a gaming universe, then Champions Online HAS to exceed its closest competition by at least the power of 2. Many, many times already I've laughed at the cleverness of some of designs people came up with. Many other times I've scratched my head wondering how did they ever do THAT?!?
On average I've spent probably a couple hours per character adjusting all the sliders to get the right look. For some I spammed the "Random" button until an interesting design came up, then an idea popped into my head about their superpower, and I went from there. For others I had a look I wanted from the start. After a couple characters you get the hang of it.
For anyone as finicky as me about character appearance, you'll be happy to know that if you play a couple levels and decide some things aren't quite right, gone are the days you need to delete and re-roll. There are "Costume" NPCs right outside the beginner area, who are always readily accessible, where you can adjust all aspects of your toon's appearance to your liking for a moderate fee.
Thankfully, I've filled all my eight character slots otherwise I'd still probably be there. With all the smart designs out there, I'm honored when people stop to check out my characters and occasionally compliment.
Open Worlds, or the Lack Thereoff:
There is one Champions server. But each quest area divides into many instances each with a pop cap of it looks like 100.
I suspect this is may be a necessity given all the character customization you have--this allows for pre-loading the skins etc. for the 20-80 or so people in your questing instance, rather than have to keep in memory ALL the cyber gloves, and mecha armor, and shoulder designs, and skin textures etc. etc.
But this fragments the community. So you put somebody on your friends list, unlike WoW servers where you probably keep running into them as you level up, in Champions they'll probably be in a different instance next time. Not that you can't see what instances your friends are in and not that it isn't easy to change instances, but staying in touch works better on paper than reality.
The good part of it is that quest areas are never dead--it is never like you are the only one there. When you need a couple others to defeat the end boss, it never takes long to get a group together. If the fragmenting of the community can be overcome by, I don't know, maybe a chat superchannel or guild recruiting superchannel that spans all instances in an area, that might correct the issue some.
One advantage of this system is, going back to character design, is that it isn't like you see the same people over and over again--with all the character designs people come up with, you can potentially see them all. It hasn't gotten monotonous yet.
Linearity:
Champions does feel more like an RPG than an MMO at times. In some ways that works since as you play through a questing instances it is almost like you are in a comic book. Going to the next questing instance is like the next comic book in the series. Still, I'm inclined to prefer the open free world of a typical MMO, but the linearity in Champions hasn't been a big stumbling block in the fun.
PvP:
Since I'm going broad with 8 different characters, rather than deep with one, I've only played the cage match, and I must say it is unique and chaotic, but by far the funnest MMO arena I've played in. It's a 5v5 deathmatch to 15 frags. Remember the cage match from the original Spiderman movie? It's a lot like that. You're transport powers--i.e. flying, superjumping, teleportation are all fully in play and quite effective. Sure, they are totally imbalanced when you see someone you are about to kill teleport away, but then you figure out you can do same...
The cage match is colorful, fast, action packed, and a lot of fun. If you jumble pro-wresting, superhero powers, and quake arena all together--that's the idea. I hope it is an indicator of the PvP experience to come. Unfortunately though, when it comes to PvP, Champions takes its cues more from the heavy defensiveness of WAR than the balance of WoW. I mean, I guess we are superheroes and all, but if you are a resilient class (i.e. heavy armor) who has buffed your defenses and liberally abuse your transport powers (i.e. teleport)--you are almost impossible to kill. If two teams of skilled players happen upon one another, the battle goes like this: each side finds the easiest member of the other team to kill, and focuses fire on that one person, over and over for 15 times until one side wins. Okay I've never seen one character killed 15 times but that is the idea. Champions PvP is unkind if you are that player.
Naturally, there is a lot of balance work that needs to be done. But so far there is a lot of potential.
Reduced Ability Set:
In that Champions is intended to be played on the XBox, you don't have a full keyboard of hotkeys to bind. So you have fewer abilities overall, a lot fewer. Moreso, your energy-gaining attack can be easily automated so you hardly have to bother with that except to occasionally turn it off. Many abilities are passive and automatic. Many abilities you can either tap OR channel by holding down the key to get different effects. If you fully charge an ability by holding it for a couple seconds, that's a lot of power ready to fire off, however if your opponent sees you doing that and blocks it, then it is all for naught. Plus you can get interrupted during a long casting time. You have to decide how much is the right amount. Plus, you have to pick and choose your abilities from a pool rather than being handed specific ones at a given level, and then you get a trickle of talent point to buff certain abilities over time. I've spent hours with character design. I've spent hours as well deciding which abilities and talents to choose. You can't have them all.
So, despite a more action-y feel than your typical MMO, Champions brings in no shortage of strategy.
The Background Mythology:
I'm almost happy Cryptic lost the Marvel license. They cheerfully revel in the B-grade-ness of Heroes Comics. The focus seems less on reverence to the source material and more on a good game.
In Summary:
Yeah, there's a lot of bugs. There is also a lot of fun to be had if you want to dive in now. Like any MMO, Champions is a big complex equation to wrap your had around--to even begin to comprehend, let alone master. It fits the MMO mold but has enough differences to be fresh and interesting.
Describe Champions in one Word: Fun.