There's really not a lot in Rach Gia itself that draws visitors -- if you're in Rach Gia, you're most likely heading offshore to Phu Quoc Island, Hon Chong and Ha Tien. However, if you miss the last boat to Phu Quoc, you may find yourself needing an overnight stay. That's not a terrible situation -- the town has a couple of minor points of interest, a few good hotels, and a handful of tasty places to get your rice. Additionally, it has a laidback, community atmosphere -- prepare to be chased by giggling children eager to practise the one or two English phrases they know.
(http://www.travelfish.org/location/vietnam/mekong_delta/kien_giang/rach_gia)