Allan Schumacher wrote...
Responding at the risk that my response somehow be interpreted as an "official" response.... 
As a show of good faith though, I'll share my thoughts. It's important to note here that I finished the game probably around the 14th, so I had heard rumors about how bad the ending was so I went into it preparing for some awful stuff to happen, which made me innately more accepting of whatever it was I was about to see.
On the whole, I found the ending to be a let down compared to the rest of the game. I think this is more of a reflection of how highly I thought of the rest of the game than anything else though. Rannoch and Tuchanka were phenomenol, and the usage of the ME1 theme at those points brings me goosebumps just typing about it now. So yeah, the ending wasn't up to the quality of the rest of the game.
I found the ending choices to be too inspired by the original Deus Ex, but I also didn't outright mind the scene on the Citadel, even if I found it strange and a Diabolus Ex Machina. The thing for me was that the Crucible was a giant unknown, so it wasn't too difficult for me to accept that it might react in ways that I didn't expect or didn't necessarily want though, so the options presented to me weren't enough to remove my suspension of disbelief. As a result I didn't mind the relays getting destroyed (I haven't played Arrival so I had no prior idea for what might happen when a relay is destroyed).
As for Joker, I didn't actually think much at the time as to WHY Joker was running, but I did find the garden planet scene confusing. In retrospect, I wouldn't have included the stuff with the Normandy because I found it confusing.
With respect to explanation, I'm assuming you're referring to some type of closure? I am not actually the type of person that needs all that much explanation of what happens after. While there's definitely a part of me that would love to know what happens in the immediate aftermath, there's also a part of me that associates the game as being Shepard's story, and that part of me likes that I, as the game player, have to make my decision knowing that I'll not know the full implications of my decision, just like Shepard. And I actually did enjoy wondering what happens to the galaxy and have had some fun discussions with some friends and co-workers about it. I think the big thing here is whether or not you believe the galaxy is totally kaput (I don't. And I'm saying that with no additional information and I don't want anyone to think that i'm hinting towards anything for the upcoming ending DLC or anything like that).
Regarding War Assets, after the game and reading some of the thoughts around the Net, I started to wonder if I misunderstood the real representation of the War Assets. I think I am like a lot of other people, in that we saw War Assets as being a kickass military asset. Though given the way the endings play out with lower war score, it seems there's more emphasis on the War Assets as a team building/protecting the crucible, as opposed to the ability to fight the reapers. I would have loved to see situations on Earth that demonstrated my choices, such as fighting along Geth/Rachni, etc. It's a shame that it didn't happen the way I had hoped.
As for "options," this is going to be a place where I likely differ in opinion from a lot of fans. I've actually always considered Mass Effect's choices to be more superficial than a lot of other people, especially when concerning the key antagonist. In the end my only option in ME1 is to defeat Saren and Sovereign. I can talk Saren down but ultimately still had to fight in in some capacity (I hated this actually... I would have loved to just talk Saren down and let that be the end of it). ME2 has some interesting reactivity in whether or not parts of your squad survive, but to me the same ultimate ending happens, just with differences in who makes the end. Only at the end are we presented with a choice and it doesn't have any effect on the ending for ME2.
So would I have loved more choice in ME3's ending? Yes. But I'd have also loved more choice in ME1 and ME2's ending, which I felt were sorely lacking. So I hesitate to state that my disappointment with ME3's choice is a reflection of solely ME3's ending. I think it was an issue with all 3 Mass Effect games.
Anyways, I am actually getting quite hungry and should go get some food. I obviously don't respond too much but I'll try to make an effort to chime in later if people have any relevant comments.
EDIT: Wall of text crits you all for 9999.... 
Thanks for taking the time to respond, and don't worry, I won't take what you said as gospel

At the risk of sounding too much like someone who shall not be named here, I always felt that in the previous ME games, it was the journey that really mattered. I'm a hardcore RPG fan (I grew up playing Baldur's Gate and Icewind Dale), and I love being able to make a game my own story, but I also recognize that at some point I do have to get back to the "real" story, especially in a game with a sequel. As awesome as it would have been in Baldur's Gate if my char could have just "Screw it, I'm on the first boat to Maztica," I knew that my own ideas about how the story should be still had to mesh with the story the writers wanted to tell.
I promise I do have a point to this

While I know that the ending of a game all about choices has to be one that ties in a bunch of different playstyles, it is ultimately everything I did up to that point that make the ending truly unique. Keeping the Baldur's Gate example: the end of ToB lets you become a god if you want to, or turn down the power and live as a mortal. On the surface, it seems like these are just two choices that have nothing to do with anything I did earlier. I could play a supervillain or a paladin and get the same two choices. But wait! If I played as a demon incarnate and become a god, the realms would shake in fear at the sound of my name. And who knows, even the evil ones could have reason to fear...just like Cyric said, I gotta steal
someone's portfolio. I could have my bro Sarevok as my evil henchman, or I could have stabbed him in the back earlier. And if I decided that I didn't want the power of a god? Maybe I decided that being a god was lame and too restrictive. What if I wanted to murder
and be a tyrant? Stay quasi-mortal and do both! On the other hand, being a good girl would usher in a new age for goodness and righteous butt-kicking, with Minsc as my right-hand man! Or I could refuse the evil taint and stay mortal with my LI. I have a small army of mods installed, so I actually got some choice, though granted my preferences are a little...unconventional. The new Keldorn LI mod is my fav so far, and I have a few saves that I run with a Sarevok one. So while on the surface the journey didn't matter much, when I get into my character's head, it makes all the difference in the world.
I have a question for you if you don't mind answering it. You said you don't mind ambiguous endings. Is there a "sweet spot" of ambiguity/closure that you like? Wether it's cutscenes, BG/DA stye epilogue slides, a mix of both? Personally I prefer epilogue slides over cutscenes. It lets me have a sense of what's happening, while leaving it open enough to add my own spin on things. Cutscenes are always appreciated, but it's so easy to make them too ambigous (I'm looking right at you, ME3), and instead of some closure with room for interpretation I get confusion.
Anyway, just curious as to your personal opinion on what makes a good ending.