In TW3 it seemed only decoctions were really worth using. I don't remember even using one oil. In the end combat was decided only by level anyway.
What was really lame was TW2/3 didn't even have an animation where Geralt applied the oil to his blade.
""An alien invasion sweeps across the galaxy. The hope of humanity rests with an exile from an ancient empire and his loyal crew. They must work together to save the human race from imminent extinction. High adventure on a galactic scale.""
In the grim darkness of the far future there is only war
"I used Quen for the most part. Yrden can also come in handy if you're dealing with specters and such."
The sequels did make some of the rarely (if ever) used signs useful, otoh they made Aard utterly useless in exchange.