That's the thing, ME3 prior to the ending, minor flaws here and there aside, was a very good and very fun game. Probably the funnest. The Tuchanka and Rannoch missions were great. The Thessia mission made me reaaaaaaaaaalllly want to put hands of Kai Leng
. Lots of fun overall.
Then the endings showed up. Not only did those endings practically render your previous decisions in ME3 meaningless, it is damn near nonsensical (even within the ME lore) way too damn brief, and nearly invalidated even the previous two games (what was the point of ME1 if the catalyst was there all along? Why didn't sovereign try to make contact with it? among many other questions).
It's no wonder Bioware did the Extended Cut and released it for free. The ending was THAT bad.
And even then, the Extended Cut couldn't solve most of the problems unless bioware did a total rewrite of the ending, from Chronos Station onward.