It seems to differ, though. ME2 was heavily tailored to characters (the main Collector story was relatively weak) and the individual character stories and recruitment/loyalty missions were, in my opinion, some of the best content in the series. Many of these ME2 scenes made you love these characters, and ME3 did an overall good job of closing many of their stories, or letting them continue. (Until the ending, of course.)
ME1, on the other hand, set up the universe, the Reapers, Protheans, all that good stuff. I thought the core story outside of the characters was very solid, while also introducing likable characters. They ARE capable (or were) of excellent core stories, and excellent endings.
The staff turnover largely had a huge impact on the series--it's a shame so many people were lost between ME1 and ME3. I wonder what the series would look like today if everyone stayed together (and EA never got involved)? It's nice to dream...