I think really the worst thing about the ending is through dialogue you create choices throughout the entire 3 games, yet at the end you met essentially a new life form, who tells you stuff and there is NO interaction at all. The actual choices are horrific, none make sense. I mean the entire(give or take) galaxy's fleet is in earth space, with mass relays gone every other home planet is essentially left defenseless, with most of the main population centre's planets burning. There is pretty much no chance for anyone to survive when you think about it.
I did the take control of them ending, and was quite irked by the lack of prologue, just nothing, where did the reapers go, did anyone ask what happened or where sheperd was. Why would the mass relays blow up, etc, etc. So I thought I probably picked the worst ending, painfully slow play through of the final 20 minutes(the latest you could save in the game before the end) pick another one, the same ruddy video with a different colour god damned energy wave, seriously, identical but a different colour energy wave?
Third I saw on youtube and was even more stupid, destroy all synthetic life, so why did Earth blow up and seemingly everyone died? I could be mistaken in that it was the Reapers explosion that killed people but they seemed to add earth turning charred which suggested the wave blew up everything?
Anyway, unquestionably there should have been a conversation with the catalyst, and some smart talking would have let a "great" ending happen, Shepard dying but taking control of the reapers and nothing else bad, or the blow the reapers up version.
THe other disappointing thing is, I saved the Rachi queen, TWICE, and all i get is a message saying some Rachni engineers are working on something I never see? I also had the "minimum" requirement for fleet strength about 3-4 hours into the game. Everything else felt like it made no impact, I had basically everything done, maxed out fleet strength yet still got a choice of 3 horrific endings?
Totally high right now, the more I think about it the more I think they utterly ruined what should have been a brilliant trilogy with token "choice based" crap in the final game, that ultimately meant nothing, pointless battles and no chance for a "good" outcome.