Yeah, the Gatecreeper is good. You probably overvalued Aetherling. Since you didn't make a base blue deck, you just have to consider Aethering as a value creature, and not necessarily warp your entire game plan for it.
I would have considered playing the Dangerous half of Armed // Dangerous, or at least made sure to bring it out of the side for grindy board-stall matchups. I'm also greedy, and probably would have played the Shambleshark. Probably to my detriment.
And yes - Trostani's Summoner is a bomb. It's almost impossible for any deck to beat that.
The comment about Aetherling hits on what I feel like is my biggest weakness as a drafter - knowing when to switch colors. I'm going to try drafting DGM more and posting them here so you guys can get onto me about how I draft, I feel like I need the help figuring out how to stay open and when to commit. I'd like to get better at this before M14, as core set draft has always been a lot easier for me.