Timeshares can be a good deal if you are an avid vacationer with a family. They usually can accomadate the whole family together, which prevents the need to rent multiple rooms. Depending on your situation, they may provide some tax benefits as well.
That said, there are many bad deals out there. My recommendation is to look at the secondary market (timeshare resales) first. They are usually a much better deal than buying straight from the property.