General:
* Critique
* Assessment
* Evaluation
* Review
* Analysis
* Comment
* Observation
Negative:
* Condemnation
* Censure
* Reproach
* Rebuke
* Attack
* Faultfinding
* Objection
Positive:
* Appraisal
* Commendation
* Praise (can be the opposite of criticism, but sometimes used to mean "constructive criticism")
Informal:
* Bashing
* Flaws
* Pick apart
* Tear down
Academic:
* Discourse
* Scholarly debate
* Analytical review
* Interpretation
The best synonym will depend on the specific context and the tone you want to convey.