Differentiating between the best Adam Sandler movies and the worst Adam Sandler movies can be a simple matter of taste (or lack thereof) which is completely subject to interpretation. No one is ever going to accuse Adam Sandler of having movies that rank in the best movies ever, but there are at least a few Adam Sandler movies that can be ranked with the funniest movies of all time, so perhaps it's best to focus there.
Many consider Adam Sandler to be an idiot genius (or idiot/genius...or just an idiot), but the guy makes some funny movies. Happy Gilmore and Billy Madison, which came right at the start of Sandler's film career, are comic legends. On the other side of the legend coin are movies like Jack & Jill.