re: Batman vs superman. Worth a watch or don't bother?

Sony makes a reboot of Spider-man, the first of which looked very good, and one where the actor finally seems right for the role.
Public reaction: enough with the reboots, we know who Spider-man is, we don't want origin tales, we want action going forward.
Marvel tosses yet another actor into the role, transposes him into their Avengers MCU, and everyone: "YAY!!!"

Batman, with even more movies to his credit than Spider-man, shows up in DC's new franchise as they build to their Justice League (their "Avengers"):
"wait, where's the standalones to establish this version? If we reboot him, we have to have his movies to flesh him out. People need to understand him and his motives."

No we don't

Wonder Woman: "so she just shows up, and we're supposed to accept her with no history, other than a single B&W photo and the in-story comment that she's 100 yrs old?"

Can't win with people; if they made the WW movie before this, you'd have a lot of folks hesitant with that. Is this a one-off, the way Green Lantern was?
GL sucked, and MoS gets criticized a lot. DC is very uneven with their movies, so maybe I'll wait to catch it on HBO, and decide from there if I want to explore the character further.

Contrast to Marvel films- the Hulk films are also uneven, the first Captain America movie required a certain taste, and lots of people didn't really love the Thor movies.
Fine- and now, you can't skip them, or the other movies going forward; not if you want to keep up with the overall story. Even if you're just an Iron Man fan, if you skip the other films, you lose a whole lot of what motivates him, as well as cameos (or in the case of CW, a co-starring role). Skip Ant-Man, that sounds safe, right? Well, not after CW it isn't.
GotG- that was just a Marvel scifi, right? Ok to skip? Nope- we get more Infinity Stone and Thanos development from that movie, than we do in the entire rest of the series.

Marvel has built a multi-movie story, that will include various characters. Sometimes, these characters will seem completely different in different movies; Tony Stark is 100% don't trust the government in the early Iron Man films, yet in Civil War he's the big Hero Registry supporter.
Some films seem disjointed as standalones, but taken in a run of films, make a lot more sense.

DC is trying to build a multi-movie story, just like Marvel. While BvS seems a little disjointed, it does make more sense if you also saw MoS. Maybe it will make even more after Suicide Squad, Wonder Woman, and the new Batman come out. Probably those films will make more sense, if you see BvS.