Roswell is one of my favorite shows, and I strongly recommend picking up the dvds. It's best watched in order, and you'll find the characters loveable even if the sci-fi is sometimes overshadowed by overblown teen angst.
As for the Roswell novels, they come in three groups. First are the original Roswell High books by Melinda Metz, which served as loose inspiration for the television series. I'm sure they're entertaining enough, but I've never actually read them, so I really can't say. Then there are the novelizations set during the television show, which vary in quality. And finally, there are the rare and elusive post-series novels, which go for a bloody fortune on eBay. If anyone happens to see A New Beginning by Kevin Ryan just laying about, please send it to me! Please?