You can't just take content from another site without permission, even if the content is user-generated.
You will first need to check the terms and conditions of the site to see how user-submitted reviews are treated. I imagine there are two common cases:
- Submitted reviews become property of the site (in the same way that if you wrote an article for a newspaper, they own the copyright).
- The user still owns the copyright of the review they submitted, but by submitting they gave permission for the site to use it.
A third possibility is that, like Stack Exchange, user-submitted content is under a liberal license that you can use on other sites (perhaps with some conditions like attribution).
In the first two cases, the content belongs to someone else so you shouldn't steal it. However you can of course contact the site in question and ask for permission to reproduce the content.