I honestly think Adam Sandler could be good, but he keeps doing "safe" low brow comedies instead of something more mature where he can show off his talent (he also asks for way too much money but that was covered in the OP). Also, he tends to ruin otherwise good movies; for example, I think 8 Crazy Nights could have been amazing if they cut out the low brow humor that ended up killing the movie.
EDIT: P.S. I'm pretty sure that he maintains his wealth through careful investing so he is not coasting off his movies. He's also a decent guy in person.