Thank you for the eloquent expression of why dark is not always best.
For me, I love ME and have since its creation. The characters and the borderline believable science backed by an exploratory galaxy whose orbit pulled me in was what kept so enthralled in the series. But it does need to be said, I'm tired of the thought process which many deem grit or being "real" with harsh overtones as a necessity.
For me to sculpt a Shepard in my physical likeness, give him my first name, choose his back story and his progression within his story, even to the finer points of selecting who he loved and lost, it was hard to sit through ME3 and not feel heartbreak for him. No, I am not talking about the high five good job heart break where the tale of your hero breaks your heart and leaves a profound emotionally scarring impact on you, one in which that resonates with fond remembrance and a longing to return to. No, I am talking about the heart break you feel when you lead the lambs to the slaughter or your old family dog to be put down. Things progressively become worse and the closer you get to that final destination you hope things end better than what you anticipate, but you know deep down it won't and the only way to alleviate that heart break is by using imaginative or optimistic thinking. Watching Shepard's end was hard for me, not because I had to say goodbye but because of the way I had to say goodbye.
I played through ME1 and ME2 flawlessly as a Paragon with 15+ playthroughs on each. I did every mission, side mission, and personal quest. I read every codex log. I explored each and every single planet. Not a single Colonist died on Feros when I rescued them. I saved the Council. Not a single squad member died during the Suicide Long Walk for me. I destroyed a Human Proto-Reaper and defeated two of the galaxies most prominent Spectres: Saren, a suicide spurred by persuasive speech, and Vaseer, by outmatching her in a gunfight. I kept my word with Wrex by curing the Genophage while maintaining Eve's life. I brokered peace between the Geth and Quarians. I ended the Cerberus attempted coup and crushed them forever on the Cronos Station. My EMS has reached 10 thousand and progressively becomes larger. I have lost characters whom I have grown attached to, such as Kaiden and Mordin, and have preserved those I could. I became a paramour with Ash Williams and began to blur the identities of these video game characters who have become friends to me over the years. In light of all this, to see my hero whom I have crafted so carefully over the years, me, having to sacrifice synthetically, electrically, or by walking face first into an explosion was.... unsettling. It is unsettling because it was so out of character.
It was out of character because all that was listed above were triumphs in dark times where victory seemed all but lost; hope, like what ME1 and ME2 ended with. And that is where the ending failed with me. A series driven by such triumph, consistently I might add, should have ended uniformly. Maybe this is why ME3 feels so different in comparison to ME1. There just seems to be a dark cloud hovering over Shepard in this finale; unrelenting and unwilling to go away. It hurt watching my hero, my personification, continually see nothing but despair and to end up dying alone and apart from his/my crew and LI, to not be told what happened to our squadmates, and ultimately what happened to the very galaxy we shaped according to our directional choice. ME3 became more of a tragedy with a glimmer of last chance goodness which you can bring about.
I'm going to end now, as this is hard for me to reflect on a series which I have held dear for five years and acknowledge its blemishes. With that being said, I do thank the staff and team for the amazing characters and moments we have been able to experience through the years. And lastly, I will echo the OP: Bioware, for future IP's please end in a manner where hope does not need to be left to the imagination while greatly emphasizing the importance of what I as the gamer did within your story and please maintain story uniformity.