Affleck brought his A game to the role itself, but the character is nothing short of awful as far as I'm concerned. That said, how much you like this Batman depends on what you're looking for. He's unintelligent, thuggish, sadistic and cruel, and fearful. But hey, he kills people, and murder makes him cool in some circles.
You can definitely argue that he has had the best action scenes, but you can also argue he doesn't. Few will disagree that the actual action choreography is the best. But the lack of narrative power means it is just kind of meaningless. Plus, his very best action scene is all but plagerized from the Arkham games, which makes it less impressive for me. Things like the Joker's "Hit me!" scene or Batman trying to figure out how solve Joker's last hostage situation had worse choreography, but were much more intense scenes for me. They set up the narrative stakes much better in other movies.
What about the costume? Well, it's definitely the most "looks like a real comic book" sort of costume, and he has a voice syncronizer that gives him a good growly voice withoutt sounding like he has throat cancer. However, I fucking hate the TDKR look, which it's doing it's best to emulate. I hate the small ears, I hate the fat bat, I hate how he looks like a gorilla in a suit. I much prefer the more realistic look that Nolan gave, though I think if they were to use the techniques that Snyder used on a different batman, maybe the new 52 one, I'd like it the best.
So yeah, it's all about what your looking for. I can admit that Affleck's batman is doing a lot of stuff well, but it's stuff I wish wasn't being done, well or poorly.
All that said, I'd like to make just say that I'm concerned that it's being received as well as it is. I don't think too many people deny that the movie as a whole was written very poorly and all the discussions I've seen centered around Batfleck regarding his positive aspects is how he looks scary and he rips people apart. Please don't take this as me saying that I am upset at people liking what I don't care for, atleast not on a personal level, but in aggregate, I don't think it's a healthy response that they see comparatively better written Batman characters in other media, and give Batfleck the nod for the sole reason that he is...well, more evil, to put in general terms. Being crueler, wrathful, and murderous are all generally seen as bad things for a person to be, and while you can argue some merits to those qualities can form an interesting character, I don't think anyone would say he's a better character. If BvS were doing something interesting with those elements, that'd be one thing, but most of the responses seem to be around "omg, I can't believe it, he just killed that dude" without any deeper insight. So as far as I can tell, people like him just because he's a worse person than the previous Batmen, and I just find that really....off. Maybe it's just shock and morbid fascination. This IS the first time we've seen a batman do these things, so maybe people just can't take their eyes off and associate that with some kind of quality, but if it's not, I'm concerned about the implications of a community that celebrates a character just because he's excessively violent. Again, not saying people are wrong for liking him, even for those things, I'd just be concerned for it as an community movement in general.