Here is a list of words you could use to describe facial expressions in characterizing and writing. See more of my writing posts here.

Gloomy
Sullen
Cheeky
Searching
Sneering
Sly
Stolid
Quizzical
Absent
Veiled
Gazing
Ecstatic
Doleful
Sanguine
Sour
Hostile
Bilious
Hopeless
Shamefaced
Roguish
Cheerless
Dour
Wolfish
Leering
Grim
Coy
Wary
Wry
Darkly
Etched
Fixed
Haunted
Petulant
Sulky
Hunted
Choleric
Unblinking
Wide eyed
Inscrutable
Taut
Peering
Appealing
Bug eyed
Agonized
Pitying
Furtive
Dreamy
Taunting
Bleak
Pained
Chagrined
Sardonic
Crestfallen
Wistful
Beatific
Wan
Vacant
Straight-faced
Blissful
Alluring
Radiant
Somber
Tight
Wild eyed
Brooding
Impassive
Glancing
Pouting
Moody
Withering
Glaring
Glazed
Scornful
Pallid
Deadpan
Blithe
Dejected
Woeful
Wrathful
Despondent
Faint
Grave
Languid
Mild
Peeved
Downcast
Black
Glowering
Snarling
Blinking
Glowing
Pleading
Meaningful
Mischievous
Derisive
Scowling
Slack-jawed
Tense
Set
Jeering