I take it you didn't watch Lost or Revolution, and don't watch Once Upon A Time or Arrow.
I watched the first season of Lost. It was ok, but I didn't feel the need to watch season 2. I've also watched all of Arrow so far. I like the show, and the first season flashback stuff on the island was decent, although the second season flashback stuff was pretty bad. I don't think I've ever heard of Revolution. All I know about Once Upon a Time is that its an ABC show that might be a fantasy show, although I'm just basing that off the title.
I don't object to flashbacks in general. I just don't want to see Xena's past. Unlike Arrow, there aren't any major mysteries to learn about her past. We were told all we needed to know about her past in her first few appearances. When she was young her village was attacked. She tried to defend it with others, and her brother died. She became angry and became a warlord, albeit one who was slightly less random kill happy than many of them. Eventually, she ran into Hercules, and changed her ways.
Now, parts of her past have been revealed and used in the show, and that's fine, but we didn't need to spend 45 minutes showing evil Xena, for example, burning down Callisto's village. We were told what happened in a few minutes, and it set up Callisto's backstory well. Xena's past is important, but there is nothing that can't just be said in a few minutes of exposition. I don't need to waste 90 minutes just to hear where she got her nickname from. She spent the time between leaving her village and meeting Hercules being evil, I don't need to see her starting wars, burning villages and killing people. I know that stuff happened, I have no desire to see it. As far as I'm concerned, her past is something to be told about to help service the stories that matter, not something to waste time watching.
Anyway, onto the Hercules episode I just watched
Once A Hero (Hercules) - Hercules and Iolaus meet up with their old friends (who we've never seen before), Jason and his argonauts. It was a pretty entertaining story, with some good guest characters and a kind of cheesy but cool fight with some CGI skeletons. Some of the city establishing shots were really bad, but the boat stuff was done well. Overall, this was an enjoyable adventure.