I still remember my first day in CoH, on a trial account way back just before issue 8 came out. I'd run out of missions to do in Galaxy City where I started and the next contat I'd been given was in Kings Row. I didn't know about the trains so I took a look at my map and oh hey, that gate to the south goes to King's Row. So off I went, not knowing the mobs on the other side of said gate would be 4-5 levels higher than me. But it wasn't them that flattened me, no. I saw and avoided them, only to be casually stomped on by a Clockwork Paladin. But that wasn't what made me want to get the game.
What made me want to get the game was what happened next. In broadcast chat I saw someone advertising a team to take down that very same Paladin. So I sent the guy a tell saying hey, I'm only level 5 but I'll lend a hand if I can. In any other game I'd have gotten called a noob and told to learn to play, or some such. In CoH, I got given a team invite and sidekicked. And so I promptly went and kicked the pants off what in any other game would most likely be a raid boss, at level 5. And I wanted to get CoH from that moment until I found a single copy sitting on a shelf in a game shop some six months later.
Nothing to do with the game's content, flying, superpowers in general. Not that at all, but rather the friendly community and the way that even back then levels didn't really matter. Sidekicking should be a feature in every game, seriously. That, global chat and travel abilities that are actually properly fast had and still have every right to be expected standard features in every new MMO, because they're just that amazing.
Edit: And I'm pretty sure I've posted all that before somewhere on these forums, so if I sound like a broken record feel free to just ignore me. :p