不怎么 / 没怎么【bù zěnme / méi zěnme】

不怎么 before an adjective means "not very". Here 怎么 asks nothing; it just tones the negative down. The register is colloquial.

Before a verb, 不怎么 means "not much" or "not often".

不太 does nearly the same job and is more neutral. 不怎么 is the more casual of the two and leans towards "not often" with verbs.

没怎么: barely, in the past

For something that hardly happened, 没 takes the place of 不.

不怎么 or 怎么不

Word order decides the meaning. 怎么不 asks "why not", with a question mark. 不怎么 is a statement, "not much".

不怎么样 is a set phrase: "not great, nothing special".