Well, I agree with almost everything that you stated and you got your wish on the Legends part.
Arrow....I loved the first two series. Then everything went downhill. The writing, the fighting and can we just stop the love interest bitching with Felicity? I'll tune in for season 5, but if it doesn't improve drastically, then I just don't have the time anymore. There's just too much great shows out there to follow. I would love for them to return to the grittyness of the first series and how Oliver really survived and honed his skills on the island. But it seems they're going the Russian Bratva way.
Flash: Loved it, still following, but it needs to improve as well.
Supergirl started off iffy, but it actally managed to capture the spirit of the comics and I'm intrigued if they can keep this up for season 2. It seems no more Cat Grant, though...
Legend of Tomorrow was WAYY better then I anticipated. Yes, the acting is hammed up, but come on! Something about this cast just clicks for me. Very curious about season 2.