There is something downright addictive about leveling up a character.
Not reaching max level, at least not for me, but simply leveling them up. Or, better, advancing them. “Leveling them up” implies “to the level cap.” Advancing them simply means I can leave off playing them after I’ve improved them in some way.
I could systematically level up my characters, one to max, the next to max, and so on. That sounds like something I’d really get bored with, though, and I think I’d quit before the first got “done.” My neurosis doesn’t roll that way.
And it’s not like I don’t have a problem leveling up characters to max, witness the sidebar list, but I never created a character thinking: “I will level him to maximum and then go from there.” Every character is made following a series, sometimes a long series, of improvement actions.
My Witch Hunter in Warhammer. I’m perfectly fine and satisfied that he’s now reached level 10. He’s got a nifty cloak on him since that was an improvement I wanted him to have and it was something I could specifially direct my activies to getting. He’s worked through three chapters worth of PQ’s in order to “close out” those chapters. He’s level 10 now meaning he’s now got a whole new bag to use. Still no hat, still no shoulders, but if I could figure out a directed course of action to acquire those, I’d do that too because that’s a course of improvement. Right now it seems it’s utterly random to get those, made worse by level 3 Bright Mages rolling need on everything in the PQ’s, including Witch Hunter gear (“Well, don’t be hating, my Whatever is Whatever level and it’s for him.”) and utter randomness only works out with an insane degree of patience ala Molten Core raiding. So last night I got him to level 10 and that opened up a new bag for him and it was good.
Then I got out my Sword Master and played him till I closed out Chapter 1’s influence score. I know I stayed up late doing it, later than I really wanted to rather, but I was caught in the grips of my neurosis. I had to reach a intermediate goal before I could call it quits. He’s all of level 6 now.
Psychosis would find me quitting my day job to reach level 40 this week. It could be worse I guess. 🙂
Kinless Chronicles 
That sounds like how I play my characters. My only 70, after playing the game for almost 4 years now, was kinda sorta an accident. I wasn’t intending for her to reach 70, it was simply an advancement I could easily achieve. And I was a bit sad once it was.
I will “advance” my alts to certain levels for specific things, like new skills or access to things such as mounts. Then they’ll sit around for awhile until I come up with something new for them to do.