Probably the best, most authentic Mexican you will get in Cleveland.
I have been to non-touristy parts of Mexico on a few occasions and I can say this isn't too far from what I would get there.
The first thing you will notice is that there are actual Mexicans dining here. Always a good sign ;) The chips are great and the salsa is HOT. Just the way I like it. I imagine you can get mild, but I'm guessing you'd have to ask for "gringo salsa" ;)
One of my favorite dishes is the Chile Rellanos. Lots of melty cheese inside. The burritos and tacos are great as well as the chicken mole. I really haven't had a bad dish. The rice and beans can be a bit on the bland side, but still decent. The guacamole is fresh and chunky. Yum
One important note, as others have pointed out, is not to expect the same quality of food at the east side location. If you want great Mexican, this is where you want to be.