Sinner Cafe is a nice mexican place in Susukino. I've been there a bunch of times, and while I wouldn't call it spectacular it's almost always satisfying.
That said, I'm British. Therefore: I know nothing about Mexican food, in the same way that Americans have never eaten real fish and probably never eaten good Indian food. I don't know if this place serves good Mexican food, I just know it serves pretty good food.
I got taco rice this time (which I have a feeling is a Japanese/Mexican concoction, but I'm not sure) but in the past I've enjoyed their tacos and burritos a great deal. Mostly the menu is pretty good value, but some things (their soft drinks for example) are just spectacularly expensive. There's a one drink minimum if you want to hang out in there too, so careful you don't get gouged with that.
It is a nice place to hang out though. It's got a shabby, arty vibe and the music they play there is often western indie stuff that I never hear anywhere else. I mean, anywhere else in the world - they played a track by Owsley one time that... I mean, I've never met anyone else who's even heard of Owsley.
So I like the place overall and it's also a great place to keep in mind if you're in Odori and need somewhere to eat and chill for a while. I have added it to my map, as you can see... here.