Generally I'm not "ending" guy, I'm "process" guy (no sex jokes, please:D). Of course it's nice to know that Jaheira and Charname lived happily ever after, but I can accept practically any ending (or lack thereof), if "the long and winding road" to that ending was interesting and rewarding. Witcher saga (books) for example. Or many historical or "based on historical" books, like Remarque's. Of course Remarque and many other authors wrote in quite specific genre, but still.
Anyway, ME3 ending, mostly after meeting with TIM is so... Well, my vocabulary is empty here and my dictionaries couldn't help me either. Strange? Absurd? Don't know, like I said, I have no proper words to discribe it.
To be honest, after I beat game, I have strong feeling that those endings were done on purpose. My three versions are:
1. Red (no pun intended) herring. Distraction. Not sure for what, though. My two cents - endings so bad so public concentrates on them, giving overall reviews like "ME3 - ending=flawless". I disagree on that - game have a lot of problems and progressively worse than ME1 and ME2, even without endings. But, with such endings public rage concentrates on them, allowing to ignore (or screen) complains in other departments.
2. Cross of Iron (1977 movie) situation. I heard that during filming that movie authors met budget issues and had no means to film ending they wanted, so they asked Coburn to improvise, thus the "laughing" ending. Not sure that Bioware "required more minerals", but if they didn't have enough time (2 years to tie all story leads for 3 games is definitely not enough), such version IMHO, sounds quite probable. However, I'd prefer to wait year more or see other ending, than to see this. However, if Bioware will follow CD Project way - give us some gigabyte "enhanced edition" patch (free of charge, of course) and correct game to condition it should have, well, I'd wait.
3. There is another movie-related legend - Russian (Soviet) director Leonid Gaidai, while making his The Diamond Arm, to prevent censorship (USSR, remember?) on his movie added scene with nuclear explosion and told censors that they can remove any scene they want, until they leave that nuclear mushroom episode in movie. Barrel roll worked - censors removed nuclear explosion scene, leaving rest of the movie intact.
So yes, ending is part of the product and should be taken into consideration as part of experience. Whether you let it slide or collect it into bottle and use to rearrenge every molecule in author's body - depends on other parts of product.
Bottom line: I do believe that that ending (not "those endings" - I refuse to consider them as "different endings") was done on purpose, to draw our attention away from other aspects of game. Such as uneven story writing - some places deserves "bravo, encore", some "meh, I've seen toilet rolls with better writing" or continuating ignorance of codex, or, or, or...