Mariscos Las Playitas' biggest "problem" (if that's the right word for it) is its location. It definitely isn't in a good part of town, as has been mentioned in other reviews. And while it might sound racist to say so, people were VERY surprised when two white guys walked into the place (or maybe, they looked at how fat I was and were scared there'd be no food left over after I had dinner ... who knows?). And also, as mentioned in other reviews, the music can be very loud and the decor is definitely basic.
Now, if you can get beyond the fact that this isn't a place out to impress you or attract middle-class gringos, who aren't happy unless everything is perfect, you'll do perfectly fine here. Yes, the location and decor are nothing to write home to mom about; but the food is quite good and the service very friendly.
I had the filet a la diablo and I asked for it to be muy picante. The sauce had the tanginess of a BBQ sauce, but wasn't sweet (and it WAS very spicy). I asked for a larger portion of salad instead of rice and beans and while plain, the lime served with the meal made an acceptable dressing. The fish was quite tasty. My partner had the filet a la Ajo, which is a garlic fish. When it came, I was very concerned, because it looked like it was buried in garlic ... and I'm not exaggerating. And while I could smell the garlic, both of us confirmed upon taste, that it wasn't overly garlic-tasting at all. Also, in contrast to other places, which use a lot of oil, there wasn't much on this fish. The garlic was far from overpowering and the rice and beans, while very basic, tasted good, too (so he told me). The ceviche, by the way, was also good.
For the two of us, the bill came to $27 total before tip and included an iced tea on it. Hardly unreasonable and the size of the portions were more than adequate. If you've read my other reviews, you know I'm constantly whining about portions not being big enough; so if I say they're adequate here, you can be sure they are unless you're an impossible glutton.
I'm not sure how comfortable I'd feel being in this area at night; but aside from that, no one made me feel uncomfortable or unwelcome after the first looks of surprise from the patrons. Perhaps there'd be a lot less surprised looks, if more people turned their mental assumptions off and had an open enough mind to try something different, somewhere different and paid this place a visit. In this case, the effort would be worth it.