I am late to the party, but mostly because I didn't like the finale, at all. I get the fanboy's enthusiasm about reappearance of cool gadgets and Nick Fury, but I was hoping for something a bit more deep, and the episode hardly delivered on that front. In fact, it came full circle and actually made some of the mistakes that initially made me give up on the show after 4th episode. Namedropping without real development, cardboard personalities, black and white heroes and villains. Urg.
The last couple of episodes have been very interesting for me because the show finally became somewhat more gray. Coulson was revealed to have been experimented upon, expressedly against his recorded will. SHIELD was revealed as this compromised agency that was brought down partly through its own lying (see: no Slingshot), evil procedures (see: experiments on prisoners in the Fridge) and ****** leaders (see: Hand willing to execute suspects and prisoners alike). The heroes were suffering without a solid ground under their feet. All that seemed interesting to me. In the finale, however, we get a new SHIELD, and most of its design failures just get swept under the rug. Coulson yells at Fury for all of 1 minute for being experimented on against his will (I am sorry, but being in a medical profession it is a very strong taboo for me), and we are supposed to feel warm and fuzzy because he is an "Avenger" in Fury's eyes. Sorry, not good enough. Fury is the coolest badassest guy there is (despite the fact that he royally ****ed up his job, like all the damage Garrett and Ward did to SHIELD does not compare to the mess its own director brought). Coulson gets promoted to Director and has not a real word of critique to the agency (like, we ****ed up big time before, this time lets do it better). They get a new base out of pure Deus ex machina, they get new dangerous tech and use it to kill bad guys for laughs, they are suddenly friends with the military and get their help.
It's OK if you like light shows and slapstick humor, but I personally only came back to because the show looked like it could finally become a good character drama. And the finale negated it all.