As a native to Southern California and a snob about Mexican food, I can confidently say that this is some of the best Mexican you'll find in Manhattan. With its labyrinth of rooms downstairs, you could easily enjoy a long night here.
Make reservations for dinner a few days ahead of time, particularly if you're in a group larger than 6, as Los Feliz only offers a certain number of seatings at certain times throughout the evening. Each room has its own traditional decor evocative of some kind of medieval, Mexican dungeon (certainly no thing has existed, but if it did, it would look like Los Feliz).
The guacamole is smooth, salty, and authentic, and each item on the menu is deliciously conceived with strong Latin roots. The best dish has to be one of the house specialities, the Quesadilla de Flor de Calabaza Suprema, made with sautéed squash blossom, finely chopped portabella mushrooms, gruyere cheese, and truffle aioli.
The margaritas are strong, but fresh and certainly creative. All in all, I'll come to Los Feliz when I'm missing the Mexican food of home and craving an exciting night of drinking, dancing, and exploring.