I wouldn't go that far, at least for most players. I think CoH added enough content, and the right content, to keep people interested over time. Personally, I think Paragon's content development speed was way too slow by an order of magnitude in terms of trying to expand the game and make it worth advertising to new players. But in terms of retaining the players it had and keeping enough new players entering to replace older players leaving, they produced the right ratio of playable content and development content. Put simply, missions verses powersets and enhancements. They were not fast enough honestly to keep people interested in just new content. And more powersets and enhancements without something new to use them on can get too repetitive. But the right balance between new ways to make characters and new things to play those characters in can multiply to make things interesting enough to long term players to keep things from getting stale.
For certain, one of the things that kept me interested in the game was the archetype/primary/secondary framework. Many games try to fill a particular niche with one or two classes, each with a few signature powers. In City of Heroes, not only could I play a controller (the AT that really captured me early in the game; for quite a while I played practically nothing else), but I could come up a metric ton of different controllers that could fill a similar role but still feel distinctly different to play. An Ill/Rad felt like a new experience after an Earth/Thermal, for example, but still satisfied the same basic need. And you can take that further: an Earth/Rad and an Ill/Thermal would still feel distinct, and even within the exact same primary/secondary selection, you could create quite a mechanically different character than someone else through your selection of powers, slot allocation, power pools, invention build and incarnates. The aesthetic customization possible in CoH was often praised as above and beyond, but I don't think the MMO community recognized how much genuine room there was for mechanical customization. This also meant that every time a new powerset was introduced, a huge number of possibilities were opened up.
I have a list of about 35 characters I'm interested in making should the opportunity arise, and I could easily make that list considerably longer. I can't imagine another game that would generate anywhere close to the same number.
I know travel powers were the initial hook for me, but travel powers alone wouldn't have kept me around as long as I did. For me the game evolved enough to keep things fresh enough to make CoH a long-term passion. CoH was not the same game throughout its lifetime, nor was I the same player. At one time, just making characters was interesting enough to keep my interest. Then it was leveling them and playing the powerset combinations top 50. Then it was coming up with invention builds and Mids-jockeying. There was a span where I spent most of my time in the Architect. And towards the end about half my time was running Incarnate trials and building up my characters' Incarnate levels. There were times I got bored with the game and took short or medium breaks from playing, and those breaks were very useful to keep from being burned out. But there was always something that changed the game for me and made it sufficiently new again that I wanted to dive back in and play it for hours on end.
I don't think I was the typical player by any means, but I don't think I was alone in this particular respect.
As I mentioned above, I tended towards controllers early in my career. This remained true to some extent throughout, but I went through phases of different ATs. It was somewhat of a surprise to me that a scrapper became my "main" over time, the character I had the most playtime on. That character also became my badger when I went through that period, which in turn got me to delve into PvP for a little while. Similarly, there were periods when I focused on incarnates, AE, invention builds, or developing a solo SG base. About the only thing I can think of that never really hooked me was the marketeering, though I certainly made use of the market.
So no, I don't think you were alone at all in that respect.
