1) They couldn't keep moving the plot forward at the same pace - needed to pick it up (they did) and then lost a lot of the complexity and ambiguity we'd gotten used to

2) They had to actually finish the damn thing - with Martin will never do. It's one thing to throw a hundred balls in the air with no intention of catching them (Martin) and another to actually grab them before they hit the floor. B&W caught a few of 'em, but no way they were going to catch them all in the time allotted.

A couple of extra seasons to watch Daenerys slowly slip into madness instead of having a switch thrown would have been nice. The Night King shouldn't have been dispatched so easily and I also think we didn't need everything tied up so neatly in a bow - leave us hanging a bit with a "shit - now what?" look on everyone's faces.