As I watched more of Ryan's films (there are many), I found this to hold true. His character in The Wild Bunch has an outlaw past, but the man we see is a forlorn turncoat hunting down his former gang and silently wrestling with what that means. His Cotton Ryan from Lawman is a sellout sheriff who eventually has to confront his own complacency. In The Professionals, he's one of four men assembled to rescue a woman kidnapped by a Mexican bandit. Each of these men has a specialty — weapons, explosives, tracking. Ryan's Hans Ehrengard's skill is horse wrangling, and Ryan plays him with a sensitivity that could mislead one into thinking he's soft — until he KO's a man over the mistreatment of a horse.
At other times, Ryan was just fun to watch. I forget where I read this, but someone said that the trick to his Ben Vandergroat in The Naked Spur was that Ryan just laughed when delivering each line, making his character not only sinister, but unexpectedly likable.
This is why, in his Western roles especially, Ryan stands out among other leading men of the genre. While I certainly consider John Wayne one of the great Western stars, Ryan displayed in his supporting parts a much greater range. (So much has been said about Wayne's inability to act that this may not be the most effective comparison, though I've always felt such criticisms of John Wayne were overdone.)
And I would be lying by denying that the little I know of Ryan's personal life contributes to my affection for his work. His tough guy credentials included being a former Marine and boxing champ, but he was also a civil rights advocate and Democrat who supposedly clashed with John Wayne over HUAC on the set of Flying Leathernecks, living for real the complexity he played on screen.