*SPOILERS AHEAD*
First and foremost, the notion that anyone would go through the financially burdening process of keeping someone alive in a prison on a boat in the middle of the ocean is absolutely absurd. If you want to make someone disappear, it would be far more practical and cheaper to just have them killed. I guess we're to assume that some criminals have too much of a conscience and decide on a more humane fate for their enemies?
Secondly, Stallone and Schwarzenegger should have switched roles. I could see Schwarzenegger playing the German/Austrian intellectual scientist type, and I could see Stallone playing a dopey billionaire. What I CAN'T wrap my head around is Stallone passing for a genius (I mean, the guy has had some great moments as a writer, but come on).
Other than that, you can expect acting and fight choreography that is bad to the point of being laughable and actually enjoy this movie for one viewing. Not worth a purchase. Rent it or wait for it on Netflix.