Hi, I'm another TWOP refugee (TWOPugee?).
Anyway, I got the distinct feeling at the end that May is not a sleeper which to me is a let down. During the few moments between when she had Fitz cornered and when she was cornered in the cargo hold I was actually excited at this twist. For them to set up her up as the seemingly most reliable character all season, have her sleep with Ward, and then have her turn out to be a major antagonist? I was starting to feel the show was turning an important corner towards being gripping. But no, it's pretty clear she was spying on Coulson for another reason, maybe for something as mundane as covering up the oh-so-horrible fact he had extensive surgery.
Real people undergo gruesomely horrible medical procedures all the time, but through the magic of modern anasthetic their memories of the event are erased. That's essentially all that happened to Coulson when you think about it. I've had two major surgeries myself without which I would be dead, and I'm grateful to the anasthesiologists who protected me from the experience. That's not to say that whatever experiments were being performed on that blue humanoid in the "guest house" were ethical, but neither was murdering two guards to save Skye.
Speaking of the show's canon Mary-Sue, ZOMG she's a real SHIELD agent now! Let's grind the plot to a halt for the first 10 minutes so everyone can marvel (no pun intended) at how wonderful she is and how she's "earned" it. Even though she's been through little-to-no real training for the job, done little in the way of "hacking" that I couldn't do with Google, and most of her supposed talent is just so much hot air being piped into the room by Clark Gregg.
Still, maybe it's Ward driving the plane now and maybe he really is a sleeper agent. That would be awesome. Not as awesome as if it were May, since she's clearly more formidable in every way, but still.