The "Legends of Tomorrow" episode had a series-high viewership and a season-two-high 18–49 rating, which tied the rating set by the pilot on January 21, 2016. The episode improved by 80 and 83 percent in viewership and the 18–49 rating, respectively, from the previous episode, "Outlaw Country", and contributed to the most-watched Thursday on The CW in four years. About the crossover as a whole, Oliver Sava of "The A.V. Club" said that the episodes did "admirable work advancing the overarching narrative while maintaining each show's distinct perspective" along with being "a hell of a lot of fun, and it's significantly expanded the scope of the Arrowverse by bringing in an extraterrestrial enemy ... There's an entire universe to explore, and this crossover has opened the door for the CW's DC shows to go cosmic in the future." According to Ed Gross of "Empire" felt "Invasion!" was a "proverbial mixed bag". He felt "Invasion!" did an effective job of bringing the characters from each series together since "the rapport between them feeling natural and oftentimes genuinely funny". Gross took issue to how the crossover was promoted as "a massive adventure" when it turned out to be "rather underwhelming. Part of that is creative—it would have been better to get a fuller understanding of who these beings really are and how they're able to know the long-term effects of Flashpoint; plus the resolution seems awfully pat ... and lacks the resolutionary scope that was expected." Gross gave the crossover four out of five stars. Collider's Allison Keene enjoyed the interaction of the cast members between the four shows, with "The Flash" setting the tone of the crossover, with the others incorporating "its light-hearted, witty banter and a fast-paced action and editing". However, the crossovers also have the ability to "starkly highlight each show's weaknesses." Keene concluded, "There are things "Invasion!" as a whole did really well, and others it didn't, with each series' strengths and weaknesses being highlighted and tested. But with each new expansion, there are things the shows can learn from, and it remains fun for fans". The review aggregator website Rotten Tomatoes reported a 100% approval rating, based on 10 reviews for the episode. The website's critical consensus reads, "The CW marshals its lovable roster of superheroes all together to quell an "Invasion!"