Let's face it, most people dont visit Maine for the Mexican food. That said, I grew up in the area and believe Pepino's to be the best option available. Servers are friendly and the food is good. Albeit a little on the pricier side for the area if you find yourself in central maine with a hankering for mexican and like me prefer to avoid fast food if at all possible, Pepinos is your place!
...in fact Pepinos Taco Stand across the river in Brewer is the better of the two. Atmosphere is typical of a tiny mex joint and friendly neighbor like service -- food is the same.