Well, this was the most comic-booky episode they've ever done... not only on this show, but on any live-action superhero television series ever, outside of maybe the Power Rangers franchise. A giant robot battle? Holy cow. They really pulled out all the stops there. I'm only disappointed that Ray didn't yell "We are cancelling the Apocalypse!"
It's interesting that all the shots of Giant-Ray were CGI -- even the close-up on his face when he was knocked out, when it seems it would've been easier to use live action. Maybe it was to maintain a consistency of focal length and maintain the illusion of vast size? They did do a pretty good job of scaling up the motion, making the giants look massive and ponderous, and giving the Waverider a sense of inertia, so that when the Leviathan swung it around in its hand, it resisted the pull and swung around slowly, rather than whipping around easily like a lightweight toy.
My favorite part, though, was how Snart won over Kassandra. I was so worried they were going to go for a torture-porn scene. I was glad that they went for a more positive kind of persuasion, the kind that actually works in real life -- and it's especially impressive that it was Snart who went the more empathetic route, showing how much he's grown. That was good to see. Though I wish they'd cast a better actress for Kassandra. That pretty much seems to run in the Savage family.
Speaking of mediocre actors, how could Carter be reborn if Kendra has been removed from time and therefore can't technically die? The rule is that the reincarnations aren't triggered until they both die.