Simple DS volume 44 the gal mahjong is a good looking title. So far as the tile layout and opponent graphics go. You can play just mahjong without the lonely salaryman minigames/features if you want but even during a normal mahjong game your immediately opposite opponent's breast will jiggle each time she picks up a tile and all 3 of the girls playing against you will comment, grunt and make other sounds that are more unsettling than erotic.
If you just want mahjong it might not be worth the 128 meg file size but I've never tried trimming it. Be aware that the lonely salaryman gameplay can unlock 'cheat' modes and such that effect your dealt hand in odd ways.
I believe you can change difficulty and tile colours in the settings but I don't read japanese. Even on what I believe is the hardest setting, I didn't feel like everyone but me was getting a loaded hand. On some Mahjong games I've tried, at least one and often two players are going rici/rich inside of 3 rounds which is just ludicrous.