I never really felt... "submerged" into the world of Xsyon, no emotional involvement whatsoever.
Never really given a reason to want to log on every day
Stamina regen was a big issue as well... If I wanted to stand idle for several minutes waiting on my char to be able to do anything, i'd be playing the Sims.
I felt the buildings overall were a big joke, no real customization, as with most everything else.

I could go on, but in ending, a lot was promised during beta, here we are months and months down the road, and i'm just not seein it.

To bring me back, I feel having some eye candy, ruins ( buildings, vehicles, random AI people who are willing to barter etc etc ) would have kept me here a bit longer, and would provoke me to log in, just to see what's up.
When playing Xsyon, I never felt like I was in a post apocalyptic world, theres no rhyme or reason to anything about it, I can scavenge tool parts that managed to survive, but there are no ruins, reguardless of back-story, or what area this is supposed to be in... This I feel, is very lame. People want to explore and discover new things, but as it stands, you can stick to one small area, literally within a few steps, and discover everything, that to me, isn't rewarding. Tree, garbage pile, dirt, water, sand... *yawn*

I'll continue to check up on updates and such of course. In hopes that this game will one day turn into something I would consider spending my time on.