Anyone know downtown Pleasanton?
Blue Agave definitely fits the "fun and cool" ticket. Sitting outside in the courtyard area is worth it alone, but the food is great too. It is higher end fare at dinner so don't go if you're looking for Fajitas or Combo Plate #2. My favorite is the Camarones Ardientes. Wonderfully large prawns in a mild sauce. Good chips with three kinds of salsa too.
I have enjoyed food at Fernandos (Mexican; 348 St. Mary's St.) in the past but the last visit was really strange. I ordered a cheese enchilada and I could swear that the cheese that topped it was American cheese... NOT a good thing. Their chips are REALLY good, though.
Blue Agave Club (625 Main St.)is pretty good but VERY pricy for Mexican food. Some people rave about their food but when I went there, my mood was for "authentic" Mexican not the "fancy" version.
I had a surprisingly enjoyable experience at Stacey's Cafe (310 Main St.) last year. Can't remember what I ordered though.
Mahalo Grille is relatively new and is also on Main Street.