I don't know who said it, but there was a quote going around that was something on the lines of "a good actor doesn't show feelings, they suppress them, as regular people do". Probably horrible paraphrasing but it's true nonetheless. How often do you really go around looking like the green lol smiley?
Steven Seagal is a master of just that, everything goes on in his head, it gives a lot more of credit to the viewers. Is he happy? Is he sad? I have no idea. Every scene with Seagal is up to debate, so much room for different interpretations and meaning, he gives a whole new depth to acting. When his character has just shot someone and he gives a badass line, is that really regret? Maybe it was. Steven Seagals physical acting is a caricatured way of acting, it's hollow and superficial. But when you go around all stone faced everywhere you can't get it better than that.
Maybe he's one of the best actors around? I'd love to see him in a film noir with limited set and budget.