For me, "playing the game" is a variable mix of costume/character design, trying various AT/power mixes to find ones I like, immersion in the game world, enjoying random interaction with other players, teaming with my friend. Basically, all aspects of the game. I just love the game, never really get tired of it. I was invited into closed beta, but couldn't get a PC and internet connection that could run it until beta went open, but I was in from then on, and I've never really stopped enjoying the game.
Kinda feels like it was fate, too: this is the only game I ever got an invite into beta for, and it was out of the blue; I live just a few miles from the latitude & longitude the devs gave for Paragon City in the old beta forums; supers is my favorite genre, and my friend and I had been disappointed with the vaporware supers games that had been promised just prior to CoH, like Guardians: Agents of Justice, and had found the single player Freedom Force to be pretty good but wanted to be able to do multiplayer... and then City of Heroes showed up.
Playing City of Heroes means spending time with something that pretty much ticks all of my boxes. I've had great experiences during The Gap, playing games like Skyrim, the Dishonored series, Minecraft, and others, all of which literally provided me with thousands of hours of excellent game time, but CoH, while certainly flawed and showing it's age, still retains the #1 spot.