We saw it the day before the Oscars. Didn't have high hopes, but wife was really excited. I can say now that I'm a happy convert and was gladly rooting for it during the telecast.
First, the negatives: it's melodramatic (aren't most Oscar contenders?); it contains too many implausible scenarios;; it's fate-driven and, tied with that, it's predictable.
I don't always hate fatalism, but the cheap notion that destiny plays as a cheap plot device makes me sick to my cheap stomach. It's why I can't stand most romantic movies, with Eternal Sunshine being a particular (and odd) exception. And this particular film... Well, let's just say, "It is written."
But yet, there are a lot of elements in Slumdog, and though some may not work so well on their own (say, the derivative gangster movie posturing of older brother in latter scenes), the piece as a whole presents a view of lower-class India that I think the popcorn-eating, extravagance-loving, song-dance-and-swirling-color viewers out there (myself included) need to confront. The whole is worth more than the sum of the parts - it's like a Frankenstein monster of a meal made out of really crazy disparate parts that you should hate (or at least wave burning sticks at madly), yet it all works together to create something extraordinary, fresh, and tasty.