First post.
My thoughts on the endings.
It was the ending the series deserved, but IMO, the endings just failed to cater for everyone. Some people would love a dark ending, some a fairy tale ending, while some others, everything in between. Different gamers have different motivations and expectations when playing this game, and the end result implied that all our choices, all our hardwork never really mattered. Bioware never gave us the power to decide how it all should go down. Instead of giving us many roads going in different directions, Bioware only gave us a road with many lanes, all going in one direction.
Now for some explanation to the ending.
Reapers exist to reap advanced civilizations every 50000 years for one singular purpose. Reapers wipe out advanced civilizations to prevent organics from reaching tech singularity, creating synthetics which will in turn, wipe out organics.
Wait, what? You heard that right.
In a nutshell, synthetics wipe out organics to prevent organics from creating synthetics which will wipe out organics.

Confused? You should be.
The only difference. Reapers seek to eradicate and harvest, in doing so, they preserve a civilization in reaper form. They only eradicate advanced civilizations, leaving the lesser civilizations intact. Whereas, synthetics, once reaching tech singularity, will eventually surpass their creators and supercede them, wiping them out completely. And they will continue to expand, eventually wiping out everything completely.
Hence, the reapers created the cycle. The citadel and mass relays were all created by the reapers, in order to funnel civilization after civilization into a singular path, predictable and can be easily countered by the reapers.
In the ending, no matter which path you take, the mass relays will be destroyed, indicating an uncertain yet promising future, a future where the reapers do not have a hidden hand in it.