I went to UAG from '99 to '03, and am now in 5th Pathway. Although Soopa is right about the Spanglish part of the instruction, UAG worked for me. I worked my butt off studying for their exams, and passed the Boards with a respectable score the first time I took it. It's my impression that at UAG, as in US schools, much of the learning is do-it-yourself. There's a lot of bureaucratic nonsense to deal with, both from the school and from the government.
I chose Mexico over the Caribbean because I wanted to improve my Spanish (I'd taken it in high school and College, but couldn't speak well), and because I wanted to bring my 3 dogs with me. Plus I wanted to drive, and ya can't drive to the Caribbean!! Re: the Spanish -- it's invaluable to me now and I expect it will continue to be so. Right now, I'm in Ob-Gyn, and I'd say that of the 7 or so patients I saw today, only 1 spoke English. And that's the norm.
I loved the people and the country and overall, I'd say my experience was positive, even though we all had our "bad Mexico days." That said, the range of responses from my friends is "despised the place; never going back" to "didn't really like it, but it worked for me" to mine, which was "I liked it and am definitely going back to visit friends and enjoy the culture."
If you have any specific questions, feel free to PM me.