People love to bash the endings of popular series.
Sometimes its justified, like with Lost. I think this is one case where it's not. Dany destroying King's Landing was one major complaint I've noticed coming up a lot, for example, even though they'd been more than hinting that she was capable of doing something like that for about a season and a half. Varys and Tyrion were really struggling to convince her to find another way.
Whatever they did, I don't think it would have been super epically amazing for most viewers. They all have their own ideas about how it should have ended.
About the only big series finale I can think of that had most of its viewers saying, eh, that wasn't terrible was Breaking Bad, going back to my childhood and MASH.