I really really likes the last stand, and I don't really know why, sure it had its cheesy moments, and there may have been too many characters, but I thought every character was really well acted and believeable. I loved Vinny Jones as the Juggernaut, the angel character, ok, it had nothing really to do with pushing the main plot forward, but he provided a solid, believable motivation for the main scientist who was in charge of the mutant research, and having beast in it was great, just for the nostagia purposes. I thought the whole Dark Phoenix plot was adequately fleshed out as well, sure cyclops got a raw deal, but that kinda led into the whole Jean might be a little bit mental feeling you got at the start, before she flipped.
I thought killing Prof X, while a serious plot point, really showed just how amoral Jean had become, and anyway, if you stayed beyond the credits, you got to see a little extra on that particular plot point...
And finally, I love the idea behind the plothole that they could have just thrown the cure kid at Jean at the end when she went loco. Had that happened it would have been Hollywood gold.