And so ends the ambitious, unprecedented four show crossover "Invasion!" event. For the most part, I would deem the whole venture a success. Though that opinion is colored by the fact that no other television series have tried anything like this before. The end of this episode indicates that the cadre of writers responsible for the entire crossover agree with that assessment on the aggregate, and so there will likely be more of these large scale crossover events to come in the future. It will probably be an annual thing. Arrow, The Flash, and Legends of Tomorrow can continue to mix with each other at any time of the writers' choosing, and now with Supergirl in the mix on the same network, it doesn't have to be limited to just Barry and Team Flash visiting Kara's Earth. Indeed, the end of this episode also provides for the possibility of Oliver or any member of the Legends of Tomorrow to interact with Supergirl should it feel necessary.    

That being said, I know that this episode is in the Legends of Tomorrow show, yet, it couldn't escape really being about Barry. The Flash hijacked another show, and while it's nice that the writers still need to address what a colossal mistake it was for Barry to mess with the timeline and creating Flashpoint aberrations everywhere, it should have been confined to his show. Likewise, since Legends of Tomorrow has time travel as the crux of its premise, it's admirable how restrained the writers were in addressing that arena of the DCW. The Legends have loads of experience in dealing with mistakes made in the timeline, much more so than Barry who made a decision that only benefitted him without consideration to others, so seeing Nate, Mick, and Amaya deal with the Dominators in 1951 was right in the show's wheelhouse.

The details of the Dominators' true purpose for invading Earth became much more convoluted after that point. Basically, it all comes down to their seeing Barry, and all metahumans on Earth at the time, as a threat to their survival. So they have come to Earth to exterminate them all. It sets up the battle lines between the heroes and the aliens, culminating in an elaborate, special effects-filled rooftop battle. The show tries to expand the scope of the battle by having Barry and Kara travel around the world to tag the other Dominators with newly-created (but untested) nanotechnology of Martin and Lily Stein's creation, but the main action is isolated to the rooftop.

The writers continually put the needs of showing the crossover with four different series over the needs and stories of this show. With The Flash and Arrow, this didn't happen. The Flash and his team had to deal more directly with the ramifications of the Flashpoint timeline revelation. Oliver and his friends were abducted by the Dominators and forced to deal with their collective imprisonment in a fantasy world. Here, the only part that related to the continuing storylines within Legends of Tomorrow had Martin interacting with a daughter he has never previously known. The writers relegate this to the status of a subplot, with Martin trying as hard as he can to avoid any sort of interaction with Lily, only to be encouraged to do so in the end by a supportive Caitlin Snow, who has her own parental issues left on the backburner.

The story at least gives the show a little bit of humanity and warmth where it's often in short supply (although that can be blamed on the time traveling adventure nature of the show itself). In the end, Martin decides to keep Lily in the timeline due to the fact that he has gotten closer to her. It feels like this will be further addressed in the show's future. Martin says he isn't like Barry, and doesn't want to make the same mistake Barry made, but this feels like Martin being very hypocritical and taking action for his own selfish gain.

The instances where the human characters recognize how ridiculous and insane their current circumstances are the few moments that make the whole crossover enterprise worth watching. Oliver and Sara do so at the end, and that feels like the writers acknowledging to the audience how far this has come from its humble, dark, human-based beginnings in Starling City four years ago. As long as the writers don't lose sight of that, I think all of these series will be just fine.