Oliver apparently doesnt believe in the existence of Batman which is a nice subtle Leaning on the Fourth Wall that Oliver is basically the Batman of the Arrowverse.
Lois clearly prefers Barry to Oliver, as his personality is closer to most of the people she knows on her Earth. However, keep in mind who Oliver is similar to, in terms of personality and ideals: Batman. In the past, Kara and others have made clear references to him on Earth-38, as Clark's friend. So, there is a chance that Lois knows him and doesn't like him very much. Basically, Oliver reminded her too much of him!
That also explains why Clark seemed ok with Oliver; he is used to that type of behavior.
Kara not revealing Batwoman's true identity to Barry and Oliver fits with her knowing of Earth-38's Batman from Clark. She's likely aware Bruce is very touchy about anyone knowing who he really is, and is assuming Kate feels the same way.
She knows what Felicity knew in the first season: it's not her secret to reveal.
So Earth 90's Flash strongly implies that John Diggle's doppelganger on his earth is Green Lantern John Stewart. Which would mean that, much like in the comics, the Arrowverse Oliver Queen is best friends with a version of Green Lantern!
The fact that Scarecrow's fear toxin brings forth Merlyn and Thawne is brilliant on a number of levels. First one being since Oliver and Barry never fully understood each other's attitudes to superheroics. Getting insight into their true feelings through the hallucinations finally helps them come to a true understanding. This is because Merlyn and Thawne knew Oliver and Barry on a personal level that no other Big Bads ever did (Except Savitar to Barry for the obvious reason). There is also the fact that these days, Merlyn and Thawne don't pose the same threat due to Oliver and Barry improving over the years. Season 7 Oliver and Season 5 Barry against the Season 1 Big Bads? No problem. An Oliver and Barry with swapped abilities that they are not used to against the same enemies? Much harder challenge, even if they technically are just fighting each other. And the fear that, given their swapped abilities and that they really haven't had sufficient time or practice to master them, that these formative Big Bads will be too much for them to handle in their current state.
Oliver-as-Barry is a lot more twitchy and panicky than normal even before he attempts to emulate Barry in his normal life. When discussing the nature of his powers Barry says that his emotional state is linked into them, with positive emotions acting as better fuel. What we're seeing is the Speed Force accelerating Oliver's emotions and thought processes past the point that he can contain them as he normally does.
In the same vein, Barry-as-Green Arrow maxes out on the dark side quickly, and sometimes in a Narmy way. Barry and Oliver have both faced their share of trauma, but by his own admission Oliver faces his inner darkness every time he fights and channels it into his blows. Barry has a long history of suppressing his issues, and the few times he does let himself loose tend to have really,reallybadconsequences. His attempts to be The Cowl come off as unnecessarily dramatic because he doesn't know how to handle those feelings any other way.
Iris having a poor opinion of Oliver for making a deal with the FBI and going to prison seems to come out of nowhere, but on further reflection, her dislike of his actions makes sense: she went through pretty much the same thing with Barry when DeVoe framed him for murder, but she and Barry actually discussed and talked through it, and Barry certainly didn't make a deal behind her back like Oliver did.
Why was Deegan able to beat Superman in a fight? In the Elseworlds reality, Deegan's presumably been a superhero for years, meaning that not only is he Clark's equal in physical abilities, if not greater, but he likely has just as much combat skill and experience as well!
Based on JWS's Flash remarks, the preview scene, which shows most of the other heroes dead, is what happened to Earth-90, which some fans remember from the original series.
The heroes slain on Earth- 90 include The Hawks, The Ray, and Jesse Quick. How sure are we that these are versions that originate from Earth-90 and not the ones that we know and love?