Adam West is the only one who seemed to ever get - and embrace - the inherent goofiness of Batman. I mean, he's a billionaire who dresses up like a BAT and fights a huge array of themed-criminals, often aided by an acrobatic orphan and a stiff upper-lipped butler. That's an incredibly goofy premise. A rich dude who cosplays and beats up clowns? Not really the best material for something super-gritty and realistic.
But best of all, Adam West HAD FUN. While future Bruce Waynes would be mired in misery and angst, Adam West was just a weird, out-of-shape dude with odd vocal patterns who reveled in the camp of the entire thing. Batman can be fun, people!
Plus, how come Batman doesn't dance anymore? Remember the batusi?