I don't think it needs a happy or sad ending, but what we got was utterly disconnected from the previous choices. When they had the sidequest for Tali and you entered the Geth cyberspace, I thought it would be connected to the ending of dealing with the Reapers. It would've been satisfying and thematic to nonstandard ways of solving problems. It also lets the Quarians have a victory that shows that engineering and creating wasn't wrong. Hell, the Geth could've worked with them and patched their history. It would reward players who maintained good relationships with their crew and make the victory a shared one, fitting with the ideal of the Citadel.

Instead, it was a one-off quest that said nothing of the the game as a whole and there were no other big choices that affected the ending.