What is an abstract noun for critical?

There isn't a single perfect abstract noun for "critical" because it has multiple meanings. Here are some options depending on the context:

For "critical" meaning "important" or "essential":

* Necessity

* Significance

* Importance

* Relevance

* Vitality

For "critical" meaning "judging or analyzing carefully":

* Analysis

* Evaluation

* Assessment

* Critique

For "critical" meaning "faultfinding":

* Criticism

* Fault

* Deficiency

The best choice will depend on the specific context of your sentence.