The good ones
Amy Adams - best look of the night.  I thought she would wear Tom Ford.  She didn't.  But I wonder if he helped with this look.  It just screams Tom Ford for Gucci to me.  Either way, I love it.  It's sleek, dramatic, chic, sexy, etc, etc.  One of her best looks ever.
Brie Larson - she's two for two this season (as oppose to last season).  I'm a sucker for this late 90s/early 00s minimalism.  The only thing - in some pictures, her chest area looks asymmetrical.  
Natalie Portman - I suspect a lot of people will hate it, but I think it's fabulous.  It's big (doh), dramatic and over the top.  Something only a movie star could wear and pull off.  And she is and she does.
Naomie Harris - I was disappointed with her GG look, but she redeems herself here.  It's fresh, outside the box, edgy, but ultimately, really pretty.  
Kirsten Dunst - normally I wouldn't care for this type of look, but I think Kirsten pulls it off.  
The bad ones
Emma Stone - after the homerun she hit at the Globes, she crashed and burned at the SAG.  I don't think black suits her to begin with (it immediately takes her to a goth/emo territory in my mind).  On top of that, this dress is as ugly as sin.  Shredded, chewed-out mess.
Meryl Streep - what a waste of that pretty Valentino gown.
Kerry Washington - a bridal gown gone wrong? This looks surprisingly heavy and not surprisingly overdone.  Also, really unflattering.  The big, too-long sleeves is the worst part.
Nicole Kidman - being edgy and taking a risk means sometimes it just doesn't pay off.  This is a perfect example.  Too costumey, too try hard, too shiny for the occasion, and finally, just plain too ugly.  
The irrelevant ones
All the TV people.