Sort of what Falconwing said.
The thing with AH2, IMHO, is that it's a treadwheel existence. A Hamster Wheel if you will.
What's the "goal"? What am I working towards?
See, that's the end really. Aces High is great for what it is. I still recommend virtual dogfighters, serious about their craft, give it a try. You will learn more about dogfighting in a month of AH2 than you will in years offline in any other sim.
But then what? I'm an example of a decade long offline player who gave AH2 a solid 2 years of my free time. I got fair at that game; not great, but solidly middle ground. Ultimately, though, after I figured out that living and dying was mostly on my terms and I started to try to figure out how to apply these skills...I felt...lost. Not that I'm some l33t pile-it or something. It's just that, I knew how to size up a fight before I even engaged, and mostly I knew before I even started what the odds were. Beating folks 1v1 or 1v2 or 2v1 or whatever combination was fun. It still is fun. But, after years, what am I working towards?
In other MMO's you work towards something. Higher levels, more gold, better equipment, cooler dungeons, whatever. In AH2, two years in, I'm as likely to beat on some n00b at Dedalos, Storch, SHawk, Steve, whatever. Get my butt handed to me. Maybe club a seal. Whatever. And then what?
Being in the game for what it is is great. But for a long term goal; to work towards some greater purpose...that's what this game misses IMHO. That doesn't make it a bad game; it just makes it not WoW.
Fun is where you find it.