AMNESIA's execution kind of reminded me of last Summer's Arcana Famiglia carrying that interesting premise and ending up being quite an annoying series. I guess there really is nothing to expect from an anime based on an otome game. Seriously.
The best thing AMNESIA probably did successfully was the merging of all routes. The sequence of the story also worked well as it gives a pretty nice development on the heroine's decisions. But for her overall character, she was barely good enough given her amnesia being the biggest obstacle in her personality development.
Setting the heroine aside, the different routes had their own strengths and weaknesses and as the series progresses, it's a good thing that each route becomes better than the previous one (excluding Ikki's route, I guess. It was just the worst for me). The series didn't had much character development giving only a couple of episodes each character. The change in their positions each arc is the reason for this which makes it a bit understandable. The only characters who were retained throughout the series was the heroine, Orion and Ukyo and all of which were pretty decent characters.
As I have mentioned earlier, despite how the heroine seems a bit weak for a main character, her development went on pretty smooth. The constant changes of the worlds she's in developed her decision making throughout the series as she tries to figure out the situations in each world she ends up. As for Orion, aside from trying to explain the situation to the heroine at earlier episodes, his character didn't really matter much in the series but the heroine pointed out at the end that he's mostly her source of encouragement. I guess that makes him a bit useful at the end :P Finally for Ukyo, his character was not fully explained until the end of the series since he was the final arc and the final guy the heroine dealt with although his constant appearances in the previous arcs were pretty interesting and very well build his presence in the series as it established things in his character.
The art of the series is pretty decent as expected from Brain's Base although dark art isn't really something I'd like to see from them, it's basically just the nature of the series itself. Aside from the characters' lack of costume change (LOL), there are scenes wherein you'd feel that AMNESIA really came from an otome game (not that I've played that kind of game).
All in all, AMNESIA is predictably a series not worth the time. Its opening episode worked itself pretty well as it gave a pretty interesting premise; continued its run in a mediocre manner with one guy after the other; and finally ending it with a decent arc but poor execution.