The place is my favorite restaurant, but unfortunately deserves a 4. As a place that runs the pocket well into fine dining, it doesn't merit any additional stars. While the design of the restaurant is elegant, the narrow spacing between tables really destroys the decor and feel of the restaurant. Standing only 5'9" I was already feeling cramped at their two person tables.
Mesa has the best appetizer of any restaurant I've been to (shy of Picasso). The appetizers on the menu are why I keep coming back. While their steak was lackluster, the Veal and Pork options on the menu are the stars on their entree menu. The seafood, while excellent, do not deserve to stand in the same light as the earlier entree options. Dessert has always been a hit or miss for the location as many of them are seasonal; if you ever cross the pound cake with a peach compote, I highly suggest you get it. As for alcohol, the place is very heavy handed (I am a lightweight though).
Service is abruptly standard fare; while I have not had any problems, there have been no spectacularly amazing incidents either.
While they are among the cheaper fine dining options in Las Vegas, their Mexican fusion is one of my favorites regardless of their flaws.