不怎么样 is a mild, understated criticism - it sounds polite but actually means 'not good.' It's the Chinese equivalent of saying 'meh' or 'nothing special.' Very common in spoken Chinese.
usage
Compare: 不怎么样 (not great, mild negative) vs. 怎么样 (how about it? / what do you think?) vs. 还不错 (not bad - mild positive).
