My group: Fighter, Rogue, Warlock, Warlord, Wizard.
After the first two rounds, the defender was down and dying (hit by the breath weapon and hit with two claws), the rogue and warlord were stunned in terror, and only the wizard and warlock were left to fight it.
The warlock put on a decenbt show, dancing round the room and hiding, while zapping it. But once the dragon put the wizard down, about three rounds later, and the defender had failed three death saves, and neither the rogue or warlord had broken out of stun*, the warlock decided to flee.
At one point, a total of 13 saving throws had been made by the group, and only two succeeded. Unfortunately these were the fighters saves aagainst stun and weakened, made while he was unconscious and dying. He didn't succeed the death saves...
So the warlock fled, but was caught in the corridor and the dragon grabbed him.
At this point the warlord had just recovered from stun, and charged the drago hitting it. This took the dragon to bloodied (the warlock had done most of the 119 points it had taken so far). I'd decided before the combat that the dragon was a coward and would flee if bloodied, and I'd modified the cave (adding tow mounds of snow that hid tunnels it could escape through), so it ran off avoiding them. (I also forgot about its free breath weapon recharge at this point.)
The two dead guys get resurrected (there was a frozen cleric of bahamut in the chamber who had been hunting the dragon, and he could have helped during the fight if they got to his body, but no-one really had the chance to do so; anyway this cleric raised the dead guys in response for a promise to fulfil his quest, and then he was able to die peacefully).
So, now the players dug throughy the tunnels, for a rematch with the dragon.
It had spent one healing surge, removing half the damage inflicted on it, and laid a trap for them (a mound of snow that it's bloody tracks led up to, so they'd all be niceles clustered around it when it leapt from ambush.
But the rogue finally made one good roll, and spotted the trap before they walked into it, and they spring an ambush of their own, pretending to walk into it.
As the dragon leapt out they unloaded into it, and during one round did over a 100 points of damage. It's breath weapon and frightening presence were less effective (each affecting a different two of the team), and then couldn't escape the fighter and get a decent distance away, so it was soon taken out.
(And I forgot again to use the breath weapon when bloodied. I'll remember for the next dragon.)
So my conclusion: this is a very swingy encounter. If you have a bit of bad luck early on, you can then be slaughtered before you have a chance to recover. If you have good luck early on, the dragon can be taken out with a bit of effort but quite speedily.
Last night, my group experienced both of those.