It's alright.  I really wish that the story wasn't so in your face about its message, because it feels kind of tired pretty quickly and doesn't hold up well on re-watch because of that.  I get it, the Doctor and the Almost-Doctor are both being of value, and there's definitely something worth exploring here but the show doesn't really engage with the idea at all.  It feels a bit silly that we kind of undermine the main theme of this episode with the ending.  It's a decent twist, but then the Doctor destroys Almost-Amy and the show kind of moves on - as if she doesn't have value and isn't important compared to the real Amy.  It's all a bit silly, even if the twists around these character's identities aren't bad.  The problem is that this is all surrounding by a story that isn't much of a pleasant watch.

The characters at the factory and their dopplegangers aren't significant enough to leave an impression, so it just becomes a kind of loud base under siege episode without any big moments to make it meaningfully distinct in any big way.  It's an episode I didn't really think much of but the more I've seen and thought of it, the less I like it.  The banter between the two Doctors felt annoying more than fun and none of the other characters feel fun or meaningful here, even Rory and Amy.  This and The Rebel Flesh feel like something that could have been decent as a single episode, but by dragging things out into two parts, everything moves way too slowly for the better twists around the Doctor and Amy to be worth it.