[noun] + 怎么样? [suggestion],怎么样?
怎么样 asks what something is like. It takes the predicate slot on its own, with no verb in front of it.
After a suggestion, 怎么样 asks the listener to approve it.
怎么样 asks what something is like; 怎么 asks by what method.
不怎么样 is a verdict, not a description: it means "not great".