I'll be in the minority then and say I liked the Synthesis ending. Thought it was a pretty interesting choice at the finale and while you could spend time poking holes at it, I was fine with the higher power explanation of the Reapers existence.
Two points I did want to comment on:
- To those arguing that synthetic and organic life proved it could get along in the form of EDI, etc. and calling that a "hole", the series establishes the Geth right off the bat as an example of the relationship between organic and synthetic life. The Prothean reinforces this with the story of the synthetics in his cycle and his complete mistrust of the Geth and any synthetic life form.
The Catalyst has thousands of years and innumerable cycles of evidence to make the assertion that the two can't coexist. An isolated incident here or there in the form of characters getting along is meaningless in the face of generations of experience. As the player, whether you "buy" into that is subjective. I was fine with it though I can see where some would see some perceived contradictions and why some would be bothered by it.
- i.e. the Reapers destroying organic life to save it being stupid and counter productive. Did folks actually listen to the Catalyst? The Reapers harvest and maintain the existence of those destroyed species. I took it to mean that they are the sum parts or a catalog/record of the DNA for each of the species they have wiped out. In the view of the Catalyst, they are preserving order while maintaining the "uniqueness" of each species all the while ascending the younger species to take their place. An imperfect solution as the Catalyst even admits once Shephard appears to change things....
Those are my thoughts at least and outside of the squad members being on the Normandy at the end (which is a bit of hole), I came away very satisfied with the finale.