First of all I want the ending to make sense and seem plausible, given the circumstances. I would also appreciate if there is enough left of the mass effect universe for future stories, with or without Shepard.
Also I want it to be an emotional experience that justifies the long journey and expectations.
I want to see that massive force to actualy punish the enemy, even if they can't defeat them conventionaly as it was said.. But From what I saw at 8000+ military assets at 100% readiness they look like unarmed civilians running a gauntless getting slaughtered where tanks and whole batalions get slaughtered by 2 or 3 husks.... Which seems anti-climatic... It just seems like it was a misstake to get a force to attack the reapers if the only one in the galaxy that can kill a husk is Shepard.. Apparently a few thousand solders commandos and tanks can't handle a handfull of em.
The troops in hammer barely seems worthwhile as cannon fodder as they are represented in the cinematics.
If they kill a few thousand husks but a few millions keep advancing then thats fair enough for a dark horrible ending... But seeing them like that is just sad

It's not heroic with a dark bitter end.. Also it woudl have been nice if you could have sabotaged the reapers coordination like you did on Virmire, even if you don't win in the end it gives a nice feel to know you did what you could given the impossible odds.
Most of all I want the end to make sense and in character for the people involved.
The logical flaws as I see them and breaches to ME lore are too many for me to line them up. That bothers me more than the question wethere it's a happy ending or not. If the reaper threat end and Organic life gets a chance to make their own way back into the galaxy then that's a happy ending, the prospect before that was a complete extinction of all life. However it woudl be nice of the mass effect universe can continue in some form or another, it's a nice little universe with lots of story potential.
The ending is nowhere near as good as the genophage and geth missions. While Iunderstand that it takes time and resorces to create a perfect ending I think it should have been worth it to Bioware considering how important it is to give the flagship story an ending that reflects the mass effect universe and storytelling in a positive way. One that is true to lore and craftmanship of the rest of the story. The genophage and geth parts were masterpieces, I wish the ending would have been as incredible and emotional as those parts. The ending is where all the previous parts of the game commes to conclution, or it should have been. All story archs leads to this point in time which makes it the most important part to get right, everyone expects it to play out in a way that makes the revious parts relevant. This is also one of the thigns peopel have questioned sicne ME1, will bioware be able to keep track of all choices and make it work until the end. Imo Bioware got very close by stumbles on the finnishing line. most of the game was incredible and you could feel that what you did had an effect until that last mission on earth and the conversation with the catalyst. Some of the earth mission was good but it needed more imo, and the catalyst part made no sense to me, it just seemed forced, I can argue that shepard had no options but to trust the reapers and do their bidding hoping for the best. But realy... What deos it matter for the catalyst if shepard made it to his home, s/he can't do anything unless the reapers tells him what his options are, which gives them all the power. They don't seem pressed enough to allow Shepard to destroy them.
And why would a free AI allow Shepard to take control? The geth wouldn't allow such a thing unless they were going extinct, last I saw the reapers wern't going extinct, the solders fightign them couldn't even kill husks... why would they be concerned. Or are they realy crazy enough to give Shepard 2 bad options hoping that Shepard will take it on her/himself to commit suicide by jumping into an energy beam and fusing all organic and synthetic life... Similar to the reaper forms that are flying aroudn killing everythign in their path... The very thing he was fighting.. even if the end movie for it represents it slightly diferently without saying what it actualy meant....
To answer the OP, I don't care as much for a happy ending as much as A Icare for the endign to actualy make sense and thus making it seem worth experiencing. Same goes for movies, some movies are great a few makes no sense at all and people hate it. I hope that made sense to everyone

most of you anyway.