Elseworlds is probably the best crossover that these series have done yet. While the main run of episodes of Arrow, and to a lesser extent The Flash, keep one foot in grounded drama, I love that they let themselves off the leash once per year and go completely Silver Age bonkers.
The one disappointment was:
As exciting as this crossover was, I was also intrigued when a certain character started dropping a certain key word that will set off alarm bells for any DC reader. And the end of the story confirms it, next season's crossover event is going to be:
Oh lordy, are they going to have the guts to follow through with all that title implies? Considering how long these shows have been running now, I imagine some of the major actors have plans to move on, so it's possible.