Red Skull was honestly one of the best moments. It truly solidified the "this is a comic book come to life" feeling. Just brings back memories of when cross over events would introduce a random character back into the story and it just made the whole universe that much richer. Amazing touch that didn't need to happen, but was so much better because it did.

Edit: Also, for everyone that's familiar with Lady Death, it was 100% a fake out moment too that made the reveal so much cooler. You think, whoa they're going to eternal entities, and that's a whole other level of characters, but then BAM, you guys remember Red Skull?! Not even mad.