Let me start off by saying I'm a big fan of SAI and have ate there everytime I've been to Disney with the family for 10 years.
When I went there the first time, I was just a little suprised that it was not a normal "Mexican" food restaraunt you find at home. I asked for queso dip and they told me that wasn't even on the menu for the kids. Kinda drained the experience. (In the past couple of years, you can get queso now though

)
But my entree saved the meal. It was phenomenal. I think I get a different meal each time I go. The food just keeps getting better and better. It helps to broaden your horizons a little bit.
This was my experience just this past February:
Got there early. The pyramid was packed and there was a line outside the tequila bar which I never experienced before.
Got seated at a table over to the right we weren't thrilled about. It's over there near the bathrooms and you just kinda lose some of the ambiance.
So just get started on some chips and soup when this lady is walking to the bathroom and falls down right behind us and hits her head.
There were so many different CMs on the scene (some security guys with devices in their ear looking like the secret service). So my family and I are still just trying to make the best of it. I HATE complaining.
Then to top it all off, apparently the lady had a few too many margaritas and puked all over the floor. The big problem with this was that you could now smell sour tequila and food while we were eating.
I flagged the manager down and told him we needed to be moved due to the smell and the sound of the woman dryheaving into a trash can (which sounded like something out of your worst nightmare)
Within seconds, I watched the manager tell the hostess, and she immediately came and got my family and I and moved us to the main dining area away from that shop of horrors.
The food ended up being the best I've had since going there. Just a great night minus the whathaveyou.
I would highly recommend, but just don't go expecting On the Border or you will be disappointed.