Ok, now that I'm level 30, i'm noticing a trend of everyone just playing dps. Thats normal in mmos i know, but in DCU, it's even more problematic because on top of the usual holy triad of tank, healer, dps, DCU adds a fourth one, called a controler. 
I have yet to meet one in a dungeon, and i rarely see any healers too (but im a healer myself), and from my little experience with lvl 30 dungeons, it seems they are as important as any other role, because the game gets HARD, if you dont play proper.
 
Controlers in this game are the buffers basically, but more importantly, they have spells to boost mana (or power) regen of the party. I can tell you im struggling like hell to heal with no regen, the game regens mana (power) by making you attack, 
as you combo you get more power, which is cool, since it mixes up the gameplay even if youre a healer, but nowhere near enough to sustain these hard hitting fights. 
Seems important for tanks too because most of their mitigation (or self heals in Fire's case) cost alot of power.
 
So if you get the game, and intend to play seriously in dungeons at level 30 (and perhaps raids why not), keep in mind that most people just loldps, so maybe you can make a difference. You can still dps fine soloing, as every class has a dps role,
 but be mindful of your second role that might be needed, and maybe spec and gear accordingly.
 
For those wondering what powers are each role, Tanks are fire and ice, Healers are magic and nature, and Controlers are gadgets and mental. Every power is DPS

I know its no use to you but im a controller and people generally seem surprised when they see me keeping power buffs up on bosses instead of just dps'in like a machine....   the game didn't do a great job of explaining what it was a controller was until I sat and looked at my powers... it just kinda went HEY YO YOU CAN SELECT CONTROLLER NOW GOOD JOB DUDE
people seem to be catching on though as i've noticed over the last few days most of the alerts i've joined have had a tank and a healer

Sounds like controllers are like the Bards were back in FFXI... I miss my bard D:

Hey, I'm sat here waiting for the good ol 12.3gb patch to download before I can sit down and play this thing and therefore havent made a character yet. So I should ask - in terms of rolling with a controller (which sounds right up my street), how precise do you have to be with your build? Do you think it'll be easy to mess it up? I've never really played a buffing role in a mmo before so I'm worried that ill feck it up.

So, they're like warlocks?
 
or priests

'Trollers are old hat for City of Heroes players.  In that game there were dps classes (blasters and scrappers), a tank class, a heal/buff class (defenders), and also controllers.
 
Initially controlling was a difficult and thankless task, near impossible to solo with, but very important if you wanted your DPS mates to approach maximum efficiency.  However, with lots of balance jiggering, and ultimately the addition of a 'containment' latent ability that doubled a troller's damage on held/immobilized targets, they became much more powerful and common.  I remember being in 8 man groups with as many as six controllers at certain points.
 
In DCUO there doesn't seem to be as much focus on class roles.  Now, I haven't seen much of the game beyond level 12 because I have a debilitating case of alt-itis and keep rolling new classes, but I find so far that with everybody having dps options, and looking at the power despcriptions, the roles are not as defined or specialized as in CoH.  Tanks and controllers in CoH seemed much more purpose-built in the way their base stats and power options combined to define their experience. 
 
I'll try to get further into the game to see what it is like in practice rather than theory.
 
I hope to see more in depth and comprehensive descriptions of the powers and abilities soon.  Any good wiki projects for the game started?

can you dual spec in the game?

"can you dual spec in the game?"

just did my first complete hard mode (hard modes are what they call the level 30 instances) and i can safely say it would have been impossible without a controler. I think its actually really cool that you need all 4 types for 4man instances (and probably 2 for raids), but it does make it dangerous if one isnt around. but i guess the same goes for tanks or healers. Funnyly enough, DPS in this game is the least important (hell our dps was a tank that since there was 2 tanks he just changed roles to dps, but his gear is tank stuff). the instance itself, Aces Chemicals, was quite good, awesome in some spots (last boss was one of the best ive seen in a mmo), and easily on par with anything wow has to offer (dungeon wise that is)

The whole group dynamic thing should be introduced way earlier.  Like straight after that intro mission it should dump you into a group instance and give you your first 'role' skill.
 
If you aren't in a group then MMOs are just bad single player games.

"@Jimbo:  Complete agreement.  I don't know why they think waiting to lv10 to introduce the class differences is a good idea.  I think the roles and useful class skills should be introduced way earlier.  Like in the tutorial they could spend a few moments telling you how your class works in a team (maybe when you're cleaning up with Supes/Lex at the end).  My highest ATM is a lv16 ice tank, and I don't feel "mighty tank" enough.  I would trade more dps for high mitigation, but what I really want are defence clickies that last longer - I took Amazonian deflection and venom injection to try to boost my tanking survival, but they fade in like 10 seconds.   Perhaps all of tanking is gear or something, but the remaining ice skills don't offer too many more tank abilities, most seem to be dps focused. "

Heres a tip dude, go to the HQ (watchtower or hall of doom), go to your wing, check out the dungeon sets. Theres a pvp set, a tier 1 set with dungeon marks, and a tier 2 set with raid marks. focus on the dungeon/raid ones, check the stats, see what you should be aiming for. thats what i did with my healer, i was getting vitality, but aparently thats for controlers only, it doesnt boost power regen from combos. Might be good to see if youre going for the wrong stats. Just a thought "

I'll be getting the game shortly, and have been looking on the web about everything to do with DC Universe Online, but still not sure what powers to choose. I am currently between Fire (Immolation), Ice (Cryogenics) and Nature (Plants). I have few questions looking to be answered and hope you guys can answer them.

Would fire or ice be better for tanking?

Is playing as a healer make it even harder and longer to get to level 30?

Is you are going to play solo, would playing as a healer be a good choice?