The dream theme is done better in Nightmare on Elm Street which came out the same year. Nightmare also have much better special effects as well. The "hippy psychedelic" dream travel was also done better in Altered States (1980) which is one crazy ride not to be missed. The whole movie made me feel like I'd seen it before and it was done better.
This is not to say that Dreamscape is a bad movie. The acting was fine but it felt like the script gave them very little to work with. Maybe it was the mood I was in when I watched it but I found the whole thing rather boring. The horror/fantasy elements are few and far between with lots of nothing really going on in the middle. Dreamscape is just O.K. and nothing more needs to be said. Spend your time watching the other two I mentioned in this review.
For more info check out the film's entry in IMDB.