I remember seeing an interview with Silmarils on Micro Kids (a French video game show) back in 1994 where they were explaining the essence of Robinson's Requiem. I was quite impressed by the complexity of the world not to mention the attention to detail. Never before was your character able to contract all kinds of diseases and ailments. Sadly enough, the game wasn't all that great. It was often more frustrating than fun not to mention very demanding. And the world you explore is pretty boring to say the least. It's definitely not a game for everyone. I'm a hardcore RPG fan but Robinson's Requiem just didn't do it for me.
Deus is an improvement, though, and corrects many of the mistakes made in the first game. The graphics are a big improvement too - much better than RR's brown shades - and the interface feels a lot smoother.
For this low price, it can't hurt giving them a go though but don't expect a walk in the park. These two games really are demanding and you HAVE to read the manual if you don't want a world of pain.