For "eager" or "enthusiastic":
* Avidity: Strong enthusiasm or eagerness.
* Zeal: Great energy or enthusiasm in pursuit of a cause or an objective.
* Ardor: Great intensity of feeling; passion.
* Fervor: Intense and passionate feeling.
* Alacrity: Promptness and eagerness.
For "sharp" or "intelligent":
* Acuity: Sharpness of vision or hearing; mental sharpness.
* Astuteness: The ability to understand and judge situations accurately and quickly.
* Sagacity: The ability to make good judgments.
* Discernment: The ability to judge well; good judgment.
For "intense" or "powerful":
* Vigor: Great strength or energy.
* Intensity: The quality of being intense; great strength or forcefulness.
For "specific" or "precise":
* Precision: The quality of being exact; accuracy.
* Specificity: The quality of being specific; particularity.
The best abstract word will depend on the specific nuance of "keen" you are trying to capture.