It's occurred to me that, for the next few episodes of season 1 that we're watching for redial_the_gate, Jack is gloomy. In Solitudes he's dying-in-a-cave gloomy, in Tin Man he's robot-who's-had-his-life-taken-away gloomy, in TBFTGOG he's AU-apocalypse gloomy, in Politics he's they're-burying-the-Stargate gloomy, and in Within The Serpent's Grasp he's Skaara's-a-Goa'uld-and-he's-attacking-Earth gloomy. Granted, two of those aren't the 'real' Jack, but it struck me that we don't really see such a long run of seriousness in later seasons (presumably because RDA doesn't enjoy acting it for long - I can't say I blame him; it must be quite wearing). 

Crack a smile, Jack - it's not the end of the world. Well, okay, it IS the end of the world...

Then again, he's never especially cheery. He's quite irritable and grumpy, most of the time. But I don't think he looks quite so consistently depressed, later on. Or am I imagining it?