I dined at this restaurant three times over the course of two short stays in Buena Vista... We'd planned on dining at Casa de Sol, but they're closed on Mondays and Tuesdays, so all the better for us. If they'd been open, we might never have stumbled upon El Paraiso.
My spouse proclaimed El Paraiso's salsa the best he's ever had...fresh, spicy, excellent. The chips were very good too, barely salted (if at all) which is exactly how we like them.
On each visit I had the cheese enchiladas with green sauce, which were cheesy and tasty. On one occasion, they were not heated as well as I'd have liked, but otherwise, no complaints.
We found the service helpful and friendly,although during the quiet late afternoon hours, the staff do tend to gather along the stairwell and chat and laugh loudly amongst themselves, which struck me as a bit unprofessional. However, we barely noticed the noise after a couple of killer margaritas :)
Speaking Spanish absolutely isn't necessary as mentioned by another poster, but a bit of Spanish certainly adds to the ambiance of a Mexican Restaurant, don't you think?