I think that for everyone growing up watching Arnies movies through the 80-90s, he always played a larger than life character; Conan, the Terminator, an ex Green Beret in Commando, an elite SpecOps warrior in Predator, a double agent from Mars... he played a character the kicked ass, took names and made it all look easy.
This has always been my conclusion. I love just about every Arnold movie, but the ones that are good are the ones where his character is larger than life.
If we don't get a 62nd ammendment or Arnold as Secretary of Energy/Environment/Green Stuff, then maybe we will get Crusade or True Lies 2. I could go for any of these options.