To see what he can do see 1940 film 'Night Train to Munich'. See it right after watching Casablanca. This is today's top tip.
Agree. Night Train to Munich is awesome.
The cast of Casablanca is a clear contender for greatest ensemble in a Hollywood movie, and Heinreid, wonderful actor that he was, is a key cog in the works. While rooting for Rick and Ilse, we also fully sympathise with the noble Victor all the way, and understand why the story must end the way it does. Heinreid is super in the role, subtly underplaying and offering a perfect counterpoint to Bogart's wisecracking.
If you haven't seen it I'd also recommend Now, Voyager as a great film with Heinreid as a very charming leading man to Bette Davis.