Him gaining weight has become very noticeable.. compare him from season 1 to now (and if you want go all the way back to Firefly days).
Well, you can attribute some of the difference between Fillion today and Fillion during his Firefly
days to simple aging. Firefly
was nearly a decade ago, after all. But yeah, even the difference between how he looked in Season One of Castle
and today is pretty striking.