This was an absolutely awesome episode.
It reminds me so vividly of Madoka Magica Episode 10. I think that Okabe and Homura could have some good heart-to-hearts, lol.
The action-packed scene before the OP rolled was particularly great, I felt. As was how much this episode did for Okabe and Mayuri's relationship, and shining light on the whole "hostage" angle in a neat way. It's very heartwarming and sweet.
Not much else left for me to add, as this was just a splendid and practically flawless episode.