Oldman is ridiculously good. A lot, maybe even most, of the big names are very very watchable, but there's always a feeling you're watching a version of themselves, no matter how good they are. I think some are just so charismatic they can't help but have that shine through through to some extent. Tom Hanks is always playing Tom Hanks, Tom Cruise always plays Tom Cruise etc. Very entertaining, very watchable and often high quality acting. But you're never really in doubt who is playing the role.
Oldman is a chameleon though. Half his films it's a struggle to recognise it's him.