User-submitted reviews

A friend of mine is starting up a website that will have user-submitted reviews. I may be joining in with him to do design/code. Everything else would be doable for me, but this I’m not exactly sure what I would do.

I think the best way to go about it would be to use the commenting system and just alter it accordingly so someone can write a review, but also have it so users can still write regular comments on someone’s review.

Does anyone have any ideas about how I could do this or if there are plugins for something like this?

Thanks