Thanks for your ideas!
However, using text will make my game look primitive and unfortunately making my own tiles just needs too much resources and time. The game I've planned will definitely mention that crawl's tiles are being used and I will openly thank crawl on my homepage as well as in my program's credits. If my game draws enough momentum then I may get enough support to create custom tiles for it. In any case this is just an open source hobby project not a commercial game.
As for "Also it's in bad taste to use another game's artwork.", IMHO the reason the aforementioned project was created was to encourage re-use of Crawl's tiles: Quoting from its home page:
In an effort to promote sharing of this wonderful resource, this project seeks to periodically package these tiles from Crawl Stone Soup's version control, and provide them in a format easily consumable by other projects.
Also, as my next post indicates I've found a few games that use crawl's tiles (one even commercially), so it should be ok.
As for "Finally anyone who finds Crawl "too difficult" shouldn't be making a roguelike of their own.", I've played quite a few other roguelikes, but none of them have been as tough as crawl. It would have been really nice if crawl had difficulty levels or such. Crawl is excellent but it is disappointing to die after retrieving three runes, and entering Zot.
PS:I dont want to start a flame war on the ethics of re-using art work from crawl. I just dont want to do something that invokes the hate of the crawl community at large, or of its devs. I only considered using crawl's tiles because of the aforementioned project, and the existence of other games using crawl's tiles which indicates that at least *some* crawl developers dont mind re-use of crawl's tiles.