Say what you will about the Flash finale but my 9 year old son absolutely loved it. I don't disagree with opinions on the ending, but having a kid next to you cheering and gaping in shock at some of the moments makes it easy to give the show a pass. It suffers, as all the CW shows do, from CWitis.... which is the need to keep the status quo (re: relationships) the status quo. Can't have the characters relationship growing and developing as that would ruin the shipping tension. Removing those types of decisions would make the shows much better overall but there's zero chance of them breaking what is obviously been a successful formula.
Looking around online, the rest of the finale wasn't even that well-received, so I get what you mean about your son's enjoyment making it easier to overlook issues if you had them. I had no problem with the rest of the episode. It sucks that someone died, but it wasn't like some Joss Whedon throwaway pointless; it was a hero's death.
But those last couple fucking minutes. If the ending had been the crux of resolving the main conflict, as it was in Supergirl, I'd have given it a pass even though it's not as satisfying. But the main conflict was already resolved, so this was just CW bullshit, blatant as ever. They didn't even have some self-awareness like the end of Luke Cage. It wouldn't have killed them to throw in Cisco saying "We're gonna find a way, Barr!" or something like that. Nope. Just do this shit so they can make up a new situation for season 4, like they did with the time gap between 1 and 2, or Flashpoint between 2 and 3. It's not just the relationships that aren't allowed to grow; it's the shows themselves sometimes.