I enjoy playing with ASCII. Never actually tried a tileset, so I can't say if I'd enjoy it as well. I like that ASCII makes my creature-modding efforts easier; just have to assign it a symbol and I'm done, instead of worrying about drawing an image...
I've considered tilesets just for the fun of it, but every time I look at a screenshot of someone with one, inevitably they do something I don't like. Like making the ohm (vanilla statue) symbol into an actual statue. I use the ohm symbol for some modded creatures because its shape to me evokes cape-like wings folded over a figure (thus I use it, for example, for a humanoid dragon species.) I don't want it being replaced by statues. Hard-setting my ohms into statues removes that bit of creativity from my tile-assigning. I mean, I could just draw them their own creature tile, but that's just a random example.
Plus I've seen places where parts of the actual text get changed into symbols too. Like a [ getting turned into a shirt, so you have random little shirts scattered amongst the text. Someone claimed to me that doesn't happen anymore, but I keep seeing things like that pop up in screenshots, so it can't be all that fixed.
Once full graphics support is in so I don't have text getting confuse'd with descriptive tiles and all that, I'll worry about tilesets more.