The first 12-13 episodes aren't the best, nothing really goes anywhere, I can describe those episodes as maybe more alike Lupin III. So if you don't have a problem with that sort of format, you'll be fine, if not, stick with it, once you get past the roadblock, it makes for some really entertaining watching.
You don't really need to have seen the OVA and movie to really understand what's going on. The show starts at Akko's induction into Luna Nova and takes off from there. However, I would recommend checking them out at least, if you can, as they're also some really good watching.
The world, the characters, the whole feel of the show clicked with me instantly. Each characters are varied, the clash between old magic and new modern traditions makes for some interesting scenarios that take place in the show.
All in all, is this worth a watch? Of course. If you enjoyed Trigger's previous works, you'll most likely enjoy this. If you're like me and didn't like Kill La Kill (the only trigger series i'd heard of before starting this), it'll probably take some time before you get into it. I'd recommend the OVA and/or movie so you can get an idea about what the show is about and whether or not it is for you.
