From what I've gathered, AMLO seems to have an extraordinarily fervent base, and he's absolutely brilliant at working a crowd and firing them up. He's especially keen on speaking to and for those who are downtrodden and living in far-out, rural areas. Unfortunately, the specifics of his promises are totally up in the air and the coalition he hobbled up this time around consists of many of those who have contributed to the problem that he promises to fix. The reality is that the massive corruption that has pervaded every level of Mexican government and the overarching influence of organized crime are highly unlikely to be meaningfully solved. He genuinely does have good intentions, but those who he surrounds himself with may be indicative of what is to come.
Despite his faults, though, it's not hard to see why a lot of people consider him the only option. Folks are earnestly hoping for a lot of change from his administration, and he has a high bar to live up to if he wants to leave a towering legacy for future generations to appreciate (Of course, among his core supporters, similarly to Trump, no matter how corrupt his administration may turn out, or how much he fails to substantially fulfill his promises, he may well continue to be the second coming of Christ).
Hopefully, for the sake of Mexico and its inhabitants, he will be able to prove his doubters wrong.
(emphasis mine) I pretty much agree with this perspective. So do ag and Hash, people with way more actual experience with Mexico and its politics. I find all the dewy optimism coming from certain sectors of the Left to be darkly hilarious. The PRI didn't die, it just went under new ownership.
