Got the Montanero plate for a sample of everything. Steak was fine, but not exciting. Salsa with chips was wierd and thin. The chicharon was not cooked quite long enough so too chewy and not crispy. Sweet plantains were done right. Rice was okay.
The place just did not have a good vibe. Sort of sad, empty and sterile. One of the servers was also a bit of a dingbat and spilled an entire pitcher of ice all over the place including me somethat.
Also on walking in the place smelled a bit like cleaning fluid and very faintly of something off instead of smelling like tasty food, always a bad sign.
The place is not a total disaster and the Montanero was certainly a lot of food for $12. But next time I am in Waltham there are 5 other places I would go first.