After playing for a month (I joined very shortly after One Wasteland dropped), I can tell you I enjoy the game immensely.
That said, I cannot tell you why exactly. The combat is a little janky, the game engine is occasionally unstable, and an overwhelming lack of endgame content leads to an endless and repetitive experience grind. On paper, I shouldn't like this game very much.
But everyday I log on, scrounge for junk, blast some super mutants, and rearrange my camp for the 1000th time. For hours. And enjoy it thoroughly.
Ultimately, I think like the game for the immersive roleplaying element; I enjoy leveling and building unique characters who each have their own strengths and weaknesses (always ignoring the "meta" builds that die-hards proclaim as gospel). I really like building camps that fit with those characters and approaching the game world differently depending on which character I'm playing.
However, I did notice that once I had a character leveled past 50 with the correct perk point distribution and camp setup, I lost interest in playing that particular character and started a new one. Lucky me that the Legendary Perk Card slots are account wide - a very nice feature for someone who enjoys leveling new characters all the time AND a decent reason to keep playing your "main" character (you unlock more slots by leveling characters to certain milestones).
I hope Steel Dawn brings more centralized end game content. My interest in participating in the immersive world of post-apocalyptic Appalachia is the main reason I log in every day, even if I don't have much to do once I'm on.
Edit: I am also a Fallout 1st member and I'd recommend a subscription to anyone logging serious hours into the game. Like all ARPGs and MMOs, the experience is much better under the paid subscription model.