Somebody already wrote up a fairly decent review of "The Girl Who Waited", so I'm just going to link to it here and let you judge it for yourself. What I write below is merely to add to what has already been written.
To begin with, I've never really understood the animosity some fans feel toward the character of Amy Pond or of the actress behind her, Karen Gillan. Billie Piper's Rose Tyler was too weepy, and Freema Agyeman's Martha Jones spent most of her time making moon eyes at the Doctor while getting all silently angsty over his inability to notice her feelings for him. It wasn't until Catherine Tate's turn as Donna Noble that I began to like the Doctor's companions again, since the dynamic of the on-screen relationship was such that I could really see some fleshing out of both characters without the annoying unrequited love thing taking over.
With the character of Amy Pond, I began to fear that the series was returning to the lovesick puppy routine, but that gimmick was quickly ended when Arthur Darvill's Rory Williams became a central figure in the show and the true focus of Amy's romantic love. If Moffat's tenure as head writer can be credited with anything good, it's the strong supporting cast for Series' 5 and 6. It is this context that I watched and liked "The Girl Who Waited", though it's not nearly as good an episode as it should have been.
I didn't like the throw-away explanation of why a person can spend literally years alone without food and water in an isolated environment while dodging badly programmed security robots. Timey wimey, wibbly wobbly stuff aside, it's insulting. I'd have preferred a better explanation of survival, maybe showing a fruit orchard that the older Amy has been raiding or something. I also didn't like that she initially rejected Rory upon reuniting with him, rather than be overjoyed. Rory literally waited centuries for her in a collapsing universe as a plastic recreation of himself who was continuously awake, retaining his sanity and love for Amy throughout all that time. She couldn't return the favor for thirty-six years, especially given what she's gone through with him and the strengthening of their bond since "The Eleventh Hour"? Come on, the writers can do better than that.
Still, for those faults, I did enjoy the dramatic dynamic of this episode. The final, heart-wrenching scene was reminiscent of Russell T. Davies' superb ability to tear out our hearts, stomp them into greasy spots on the ground, pick them up and reconstitute them, put them back in our chests, and start the whole process over again for the next episode. But then there was the logical question that sprang to mind: why is Rory so broken up when he has managed to rescue the Amy he knows and loves? And that killed the moment for me as a punch to the gut. (Now don't go complaining about a spoiler — if you don't know by now that the Companions, with rare exception, get a Hero's Death Battle Exemption every episode, you really should pay more attention.)
I give "The Girl Who Waited" a C-, which is a pretty generous grade in my humble opinion. It's saved by the talents of Darvill and an ever-improving Gillan, but excellent acting can only go so far with a story this weak.