I don't own ME3, and I obviously have not played the endings myself.
But I do own ME1 & 2, and I have played both quite a bit. I have several Shepards, all of whom I'd love to play their stories to a conclusion with.
I've been following the controversy about the endings quite closely, despite not being directly affected (yet). Partly because it invokes my sympathy for the fans after getting badly burned by the Dragon Age II ending myself. Partly because I really want to play the trilogy to the end with all my Shepards.
However, as the ending(s) are currently presented, I have no desire to purchase ME3; I simply couldn't bear the culmination of all my experiences as Shepard to end like they currently do. It would be all the pain of DA2 all over again, only worse.
Others have already expressed many of the issues with the ending more eloquently than I could (moreso since I can't very well discuss the details here in the non-spoiler forum). I can add little to that beyond agreeing strongly with their reasoning.
For me to purchase ME3 so I can finally play the trilogy to it's conclusion (and trust me when I say I really want that), I feel two points must be addressed; without them, I'd rather end my involvement in the franchise where it currently is.
1) Closure.
I absolutely need to know what happened to every one of the characters I have connected so deeply with over the couse of the game. Shepard & LI foremost, but the rest of the crew as well, and not in the form of an uncertain cliffhanger. Also, the reapers, the other races and galaxy at large would need closure beyond the current level.
I personally felt DA:O's epilogue sequence and slideshow was a good way to accomplish much of it, but I am no writer, screenwriter; I'm sure there are other ways as well.
2) An option for a happy ending.
Maybe not rainbows, unicorns and disney weddings, but at the very least Reapers dealth with, Shepard surviving and re-united with her LI. I don't particularly care if people call it cliche, I don't particularly care if it's not angsty enough to be art. It works well, it gives me a sense of accomplishment and a satisfactory ending to at least one of my Shepards, and I feel it fits very well with the theme of hope and struggle against the odds which has been prevalent in the series.
I've read plenty arguments about how sacrifice is a big theme as well, and plenty people have expressed that they didn't expect (or even desire) Shepard to survive the final hours. However, I never saw it that way; my paragon Shepard always held hope, fought hard against the impossible odds and came out on top in the end every time. The climax of ME2 pretty much exemplifies it; through making the right decisions and fighting hard, I saved most of my crew, defeated the collectors, foiled their plans, defied Cerberus and none of my squad died. I accept that the cost may be higher in the conclusion of the trilogy, but I in no way expect or take it for granted that Shepard wouldn't come out of it on top.
Casey Hudson writes that you intended us to experience an inspiring and uplifting ending. I applaud that sentiment, but not only are none of the current endings what I would consider remotely inspiring or uplifting - I really don't think I could find an ending where Shepard makes the ultimate sacrifise to be uplifting at all.
You gave us the choice in DA:O so beautifully; the Warden could survive the archdemon, but at the cost of either the dark ritual or the sacrifise of another warden. This is the kind of choice I expect to make in ME3.
I'll end with a quote from the from Brent Knowles, lead designer of DA:O, because it expresses so well what I'm trying to say:
In general I'd say a Role-Playing Video Game Trilogy Ending should (try to) do the following:
1. Reward the player's choices throughout the series. The big stuff they did should be noted. They should *feel* like they had a unique impact on the world.
2. End on a positive note. This is really important for video games...life in general is full of s****y stuff happening all the time. When I invest a hundred hours into a game I need to walk away feeling like a hero.
When you waste a couple hours of a person's life with an artsy/depressing movie or short story or even a novel, it is more forgivable because the time spent is less. And presumably the consumer knew what they were going into when they started. Certain directors create certain styles of movie. Certain writers write specific types of fiction.
On the other hand somebody playing an epic role-playing video-game trilogy is going to *expect* to be the hero and save the universe. That's why they are playing the game. When expectations don't match reality, disappointment is created.
I really hope you're listening to your fans and it results in changes. I really, really want to finish the stories of my Shepards from ME1+2. But not in the way the their stories would currently end. ME3 remains a no-deal for me as is.