Very little happening has always been the biggest flaw of Busiek's writing. The guy can't do a major event to save his life. I don't mean he can't do it well, I mean he simply can't do it, period. People went gaga over his Avengers run only because it had been so long since the book felt like proper Avengers that a return to an iconic line-up and iconic storytelling became an event in and of itself.
But look past that, and you soon see how unimportant in the grand scheme his stories were. The core concept of the book when he started was still the same core concept when he left. Nobody died, there were no big events, the title didn't have any major ramification on the greater Marvel universe, etc.
This is especially noticeable when you compare it to Bendis's Avengers. As bad as Bendis's work on the book is, in just his first few issues, he gave us Dissambled. And for all that storyline's flaws, it's undeniably more of a foundation-shaking event then all of Busiek's run put together. The Avengers in Bendis's hands is, without a doubt, an important book. Quality of the stories aside, Bendis is giving us Big Events, capital B, capital E, something it never felt like Busiek was even trying to do.
At least with Bendis's run, you can genuinely say the Avengers' world will never be the same again. Who can say that about Busiek's run?