The folks who make the rltiles project clearly do not understand the meaning of "public domain."
Specifically, first they say the tiles are in the public domain, and then they say they want you to include a license notice.
Problem number one: Public domain varies from country by country and some countries don't have it at all. It would have been better if they'd used a Creative Commons "0" license.
http://creativecommons.org/publicdomain/zero/1.0/Problem number two: Public domain means you're free to use it without attribution. That means there is zero legal requirement to state you got the tiles from the rltiles project.
This means that while it's a dick move to use the tiles without mentioning the rltiles project at all, there is no legal reason for you to do so. Since they say the tileset is in the public domain, they have no legal recourse to make you attribute them.
Personally, my problem with raster tiles is that they're hard to distinguish. (Much harder to distinguish than font glyphs or simple vector tiles.)
Do I care if it's a common tile set or a custom tile set? If you're using a common tile set then it's less likely that I'll miss the two pixels making monster A different than monster B. By that count I have no problem with common tiles.
In general, the cost versus benefit of custom tiles doesn't pan out for smaller Roguelikes. If you've a coffeebreak Roguelike and the only difference between it and any other game is the tiles, you're doing it wrong.
A lot of folks leverage existing tiles. Andor's Trail, an RPG for Android phones, (available at
https://play.google.com/store/apps/details?id=com.gpl.rpg.AndorsTrail&hl=en) mentions that it uses some of the tiles from rltiles, in addition to other tiles from other sources.
Focus on the gameplay. If your game plays identically to other Roguelikes it is going to be ignorable regardless of the source of the tiles. If your game play is awesome it is just possible you could get a artist fan who wants to contribute with custom tiles.
Cheers,
Steven Black
