Well, of course the critics hated it. This isn't a movie that's going for the big-time critical acclaim. But the fact is that it's really very good.
Sure, if you don't like that Chris Farley brand of physical comedy, or the exceedingly dry wit of David Spade, you're not going to like it. But for the rest of us, the movie has many hilarious, and for that matter quotable, sequences, and the plot isn't half as dumb as that of "Black Sheep." The parts that aren't meant to be humorous are actually done well, not what you'd expect from a movie of this ilk, and the acting is really pretty good.
"Tommy Boy" is without question Chris Farley's best movie. I give it an A and suggest you give it a view.