I agree that Desmond didn't need to die, but the rest of the ending could be a set up for sequels (AC4 anyone?). For example, a new protagonist could use the animus to try and find a way to stop Juno from taking over the world.
That actually sounds kinda stupid, but I'm sure UBISoft can come up with something better.
Now, the world don't move to the beat of just one drum, What might be right for you, may not be right for some. A man is born, he's a man of means. Then along come two, they got nothing but their jeans.
But they got Diff'rent Strokes. It takes Diff'rent Strokes. It takes Diff'rent Strokes to move the world.
"invade some poor sap and jihad bomb him" - LazyKenny
To me, the real reason is that it's anti-climactic. After 5 games of amazing plot & action, you expect a little more than for the main character to have a 2 minute conversation w/ a ghost, touch a ball then take a nap...
The way I see it is a cliffhanger leads to continuation of a story, not a crappy end to one. That's just me though.
They may somehow continue it, but they have stated that Desmond's story is over. It was a bad way to end HIS story IMO. I dot even mind the way it was written. It was the execution that I found anti-climactic & rushed.