I don't mind the graphics, they actually make the outside look like a landscape, and ASCII really isn't that bad of an art form. I've actually never played another ASCII game, and, for example, I can't stand Nethack, which I play, in ASCII form. DF really has a great implementation for it.
Probably the only thing that could be improved is that that the game has so much, but most of it cannot be modded. I love the background music, and the sandbox feeling is amazing, but that kind of ends when you go into the raws. I can't make sniper rifles that are extremely accurate, I can't make a creature have no attacks (Pushing is still and attack, people), and even though I know it's changing in the next release, I can't make custom workshops, I can only add in new reactions in the smelter, and the tags have no explanation, so for some of the features it's like not even knowing. Even the wiki doesn't have them all. It's actually a really small gripe which shouldn't be a big priority, but it's still something.
Love the game, Toady! Keep it up!
EDIT: Oh yeah, and the arrow keys being tied to number keys really messed me up. I had right and secondary down be the same key for weeks, which was horrible. I didn't even know I could change it to + for the longest time, because I thought "Oh, it's already assigned to +, and it still doesn't work. Darn, looks like it'll have to stay."