Movies like this are a one-in-a-generation affair. The Last Airbender. Catwoman. Batman and Robin. You can't call it inept, because there's clearly some talent involved. You can't call it badly acted, because Henry Cavill and Ben Affleck are doing their best. You can't even call it dumb, because the director clearly wants to make a point.
But Batman v. Superman: Dawn of Justice is a movie, from beginning to end, that just fundamentally does not work, and aggressively doesn't work. It's a nightmarish apocalypse of a movie, a mishmash of Greatest Hits that simply doesn't understand why the original stories worked, so desperate to set up a world it falls apart under its own weight, so confident that its message is worth telling that it forgets what it's saying and focusses on making it look good instead, so desperate to be taken Seriously that it becomes a dreary brown mess. There are a few highlights. Gal Gadot is great as Wonder Woman, and surprisingly, Affleck's interpretation of Batman works. But they deserve to be in better movies than a movie that hobbled the DC Cinematic Universe until it shuddered to a halt with Justice League, and now awaits an upcoming reboot.
If you're able to appreciate bad movies, it's worth a rental. Rifftrax has done a very funny downloadable commentary if you want to laugh. If you're fan of Superman or Batman at all, skip to the at least workable Justice League.