Apologies if this has been covered elsewhere.
There were a number of things that made CoH great, first and foremost the teaming - it was just fun. Sidekicking and exemplaring meant anyone (pretty much) could team with anyone else and teaming tended to benefit people due to the nature of the missions.
One of the other factors I think that impacted on the above was the limited penalty for dying. There was no equipment damage incurred by dying, just debt which lets face it, could be burnt off fairly quickly. You didn't have to exit the mission to go and repair and thus interrupt gameplay. It just halved the speed of your leveling for a bit.
Additionally, due to wakies, player rezs and, at worst, the hospitals there was no huge delay on respawning and very rarely any amount of running back from a hospital to the mission entrance. Even if you did need to run back the travel powers made it pretty quick (I'm ignoring the first incarnation of the hollows here - shudders) [a team mate with tp exiting the mission to port you was always nice as well)
I think that these two together combined to mean that, though not a happy occurance, even a team wipe wasn't a major issue, game play wasn't overly interrupted and people didn't get angsty with one another for being a n00b and ruining the mission. within minutes you'd all be rezd and ready to have at it again. This is in turn part of what i think helped make the game so friendly and encouraged teaming.
The point of this post? - CoT please don't have death overly impact on the gameplay, yes there should be a consequence but i think CoH proved it doesn't need to be particularly detrimental. I can't be doing with mmos which make me run for 10 minutes before i get back to my body and can rez. It's just not fun.