Not too hot. We were asked if we liked them hot but alas, they were mild. Mild and delicious. I had a lengua, carne asada and adobada taco. The lengua and the adobada were great but the asada, like the El Rey truck on Chinden in Garden City, was made up of really small peices of meat, so small in fact that if it weren't for the tortilla chewing would be optional.
Update: I forgot to mention that this truck is in a Pennzoil oil change parking lot so next time you get your oil changed you might want to chose your changer based on its proximity to tacos.