When I got the M64 console, Xibalba 64 was an easy pick for me out of the four games available. I bought the M64 console and, out of the four games available, I had no hesitation choosing Xibalba 64.
It's definitely not a killer app, and neither the graphics nor the gameplay brings anything new to the table. It's basically a Doom clone, without even the ability to aim vertically. So why did I choose it? Because I love FPS games, they're pretty rare on the N64, and the ancient Mayan setting really appealed to me.
The game runs incredibly smoothly, controls well, and is genuinely fun to play. The graphics are extremely basic, but everything else works like a charm.
The multiplayer modes, supporting up to four players in couch co-op or versus play, are something special: pure arcade fun, just as gaming should be!
If you enjoy FPS games, give Xibalba 64 a chance. You might be pleasantly surprised!