I do have very lucent dreams, but they aren't crazy at all. In fact I like that I can recall them, and tell them to others the next day. They are usually kinda funny. haven't had more than a handful of nightmares (usually more anxious than scary) dreams in a few years.
but like with any drug or endogenous substance (melatonin is exogenously produced as well) it affects everyone differently
My fiancee can't take it on work nights, because she is groggy on it for a few hrs after waking. I don't have that problem.
But I always recommend melatonin to people with sleep problems, before over the counter or prescription stuff, as it is a bit more natural, and easier to quit