Garrison
Well have to disagree with you there. S6 wasn't great but I found S5 so badly flawed. So many irrational situations. For instance how Glorie is a god but you can permanently get rid of her by killing her alto-ego! Or if she opens the vortex to return home why not do that rather than keep it open, which would destroy all universes?
Most of all it needs the blood of either Dawn or Buffy to close the vortex. However I know of no reason why it needed all the blood of one of them? Buffy could have just cut herself, bled until the vortex closed then gone home.
Steve
The whole season was a build up to a sacrifice. Gloria is a Goddess in exile. That limits her power. When you bring God into a story logic always goes down the drain. Watch what happened with Supernatural when Castiel become God. Silly season.
Up until season six was announced it looked like it was to be the end of Buffy, with someone else becoming the new slayer in yet another spin off...
They could have "the new slayer" like Dr Who has "the new Doctor" every 3/4 years. But they decided to play it safe and keep SMG as an anchor for the show.