You're not going to find tacos garnished with lettuce, tomatoes and processed cheddar cheese at this little Mexican hole-in-the-wall. Rather, they will be appropriately topped with chopped onion and cilantro, served with a a wedge of lime, as God and Mexico intended.
Cinco de Mayo is serving, among other Mexican dishes, real-deal tacos. Soft, warm, corn tortillas, topped with a meat of your choice. Choose from a list of about 6 or 7, which includes tongue, chorizo, "salty meat," and the I-have-yet-to-try beef head (they didn't have it on my last visit).
The place is set up in what was probably an old luncheonette. A long, narrow room, with an equally long counter, behind which your food will be cooked to order (OK, more accurately, the meat will be reheated to order). And they have that Mexican Coke, if that's something that gets you all excited (it shouldn't).
While Passaic and Paterson have their fair share of places like Cinco de Mayo (Brenda Lee comes to mind), you don't find them tucked away in Bergen County very often. And that makes this place all the more special.
It should be noted that this Hillsdale Cinco de Mayo has a different and better menu than the Cinco de Mayo in Waldwick, and I don't know why.
Oh, and there's a related Cinco de Mayo market right around the corner on Park Ave. Lots of Mexican staples here.