Bosh is a good player. Bosh was a good player when he was here. But he was nothing special. His game, as a whole, is replacable and thats why he was never anything extraodinary or unbelievable by NBA standards.
He was/is a very good mid range shooter for a big (or even a player in general), who can handle the ball well enough to use that mid range game to penetrate. That all lead to a very efficient offensive scorer. But he was an average rebounder, an average defender (as a whole. Weak man to man, but good at help D), not much of a passer and has a limited post game (mainly because he has trouble getting deep post position).
Bosh was the classic 'good player on a bad team'. He was never franchise or superstar material, he would have been a very good #2 as a secondary offensive threat, who didn't hurt your team anywhere (specifically when he can play the 4 - a bit more dicey at the 5).