I've played all three games.
One of the things missing from CO and DCUO is storytelling. Sure. They have storylines. But they aren't expressed well. And in both games, there's terminal over-use of "Get me X number of bear asses."
Don't get me wrong. CoH has it's own "Bear Ass hunt" missions too. But they're spaced more judiciously. With a lot of "Kill X" being relegated to optional badge content.
Another is a nice, consistent control set.
Yes, you can reconfigure how you move and what you see in CoH. But it's still internally consistent.
CO and DCUO suffer because of "console compatibility" choices. It's not that I begrudge console players. It's that the choices made to try and accommodate that niche has actively damaged (and limited) usability on a PC.
Another is developer-to-player engagement.
Let's just say that Jack was never really a "people"person. Even in person. Sure, he can dial up the "schmooze" for conventions and PR. But he's really a fairly antisocial person at heart. This is why he was so bad at player engagement. He was a big believer in "The devs are Gods. The players should just be grateful." paradigm.
And CoH just NEVER worked that way. A huge chunk of the team was actively engaged with players from the get go. And it became even moreso after the advent of the Paragon Studios era.
CO is still locked in this. Mainly because their dev "team" is essentially one person, with responsibilities elsewhere in the constellation of properties. When the position isn't empty.
Funding is nonexistent for development. And the only push from the parent company is "new lockboxes".
DCUO? I honestly don't know about community interaction. During the 6 months I gave the game, I became convinced there is no "community", in the CoH sense. The devs were unknown to me. And with the rather sparse (and hostile) player-to-player environment...
So, CoH has been the only thing I've played regularly since July 4ht 2008 (when I joined).
I have a CO account still, that I peek in on every now and again. Because I have a lifetime sub (traded for swag w/Jack at a GenCon). I peek back in ever 3-6 months to see if I know anyone. But beyond that...nah. I've already done 99% of the content in the game, and it just isn't that replayable.
And I haven't even bothered to look at DCUO in a long, long time. That's how bad a taste it left in my mouth.