Ben's matured a lot since the Armageddon/Bennifer days. He's a decent actor and a good director.
Batman doesn't require some incredible performance to pull off, Affleck will do.
I really loved Nolan's take on the Batverse, but I'd like this version to be a little lighter and a bit more fun like the Arkham games (as in Batman actually has a Batmobile, not a military tank). Just not as campy as Batman & Robin obviously or even the Burton films.