Just bumping this thread (and renaming it for accuracy, as hef pointed out).
It's a bit annoying that here in the UK we're mostly pretty behind the US with these shows. Channel 5 has only just started the second part of Gotham s1, and I think we're two or three episodes behind on Arrow/Flash as well.
On Arrow/Flash, though, I'm really liking them. Arrow is still keeping up the excellent quality they've had from the start, and while I thought the Flash was a little too cheesy at the start, I think it's settled in really nicely. Yeah it's still that bit lighter than Arrow, but I think it's found its niche and is getting the balance pretty good. I've also really enjoyed the cross overs so far.
On which note, have people been following the news of another spinoff show that will star a team of heroes? Looks like it'll involve Brandon Routh's Atom, and apparently Caity Lotz is meant to be in it as well, so not sure how they're planning to bring her character back to life (unless something has happened in a recent episode that the UK hasn't caught up with yet!). Could be really fun though, I like the richness that these crossovers bring. (EDIT: Oh and although Supergirl is going to be on a different TV network, apparently they're talking about working together to also be in the same universe as Arrow/Flash).
As for Constantine, I thought the first season was solid. Not mind blowing, but it was definitely quite different to the others, and surprisingly full-on horror film style at times. I haven't seen any news either way about cancellation or renewal, but I'd be keen to see more.