It is very important for the main description to be unique more than anything else. The worst thing to do here is to have the same copy as other products as that will devalue both pages for using duplicate content. This needs to be at least 50 words in length for it to be relevant. That is about as long as this is up to here.... Use of "keywords" in here is helpful for search (ie "low deflection, pool cues, billiards) but you don't need to over do it. It should sound natural and explain the benefits of the product and why the customer should buy it. looking at similar products reviews is a great way to get some ideas about what to write about if you are having trouble.