With most roguelikes there's too much information on the screen to convey with most tilesets. Nethack and Angband notably have terrible default tilesets that are far harder to decipher than ASCII. When you add the opacity of those roguelikes (Angband is a bit better, anything you experience is permanently added to "memory" in your save file, but you're still blind in early encounters. Nethack is just obscenely opaque about everything)
Crawl strikes me as a roguelike that does well with a tileset. For one, the tileset is great, going as far as WYSIWYG weapons on monsters (The tile changes depending what the monster is wielding), with big easy to read tiles and a whole bunch of extra enhancements, like mouse support. Plus, Crawl's very transparent, it gives information readily, so you're never in a Crawl or Nethack situation where you have no idea what this little green iguana thing is until it hisses and now you're turning to stone.