yeah but it is the future in Doom, think about, Doom guy has to be able to use all the technology at his disposal. I believe that Doom guy is highly intelligent compared to Harry Pothead and the governator. Think about it all those computers in the UAC base and he knew how to use them. While not being up to the same level of intelligience as the scientists he was protecting he probably has a good understanding of how things work around him. The fact that he was smart enough to pick up PDAs and read the data entries in them to learn what is happening in Doom 3 proves his intelligience. He probably has very good control over his body and reactions as well. If you saw a Demon from hell you would probably freeze up. Not the Doom guy though. He doesnt let his adrenaline cause him to be uncontrollable.
Harry Potter may have a good book knowledge but the fact is that he has just that book knowledge. Harry Potter may have used his "magic" to fend off small foes and do well in school, but the Doom Guy handled a much bigger situation much better. Honestly when has Harry ever had to fend off a demon army from Hell.
In Predator Arnolds character played more of a grunt then Doom guy. Arnold just ran around the jungle fighting one invisible Predator that managed to kill his whole squad. If he where presented with something that required him to interact with something other than weapons such as computers he probably wouldnt be able to succesfully accomplish anything that would aid his survival.
also Harry potter being thrilled that Doom guy was gonna stick a wand up his a$$ is funny.
Also as another thing proving Doom guys intelligience. He may not be intelligent in the areas of science, but marines have another kind of intelligence. They know how to handle themselves in combat situations. Most can do some kind of first aid on people who are injured. They are trained in Battlefield tactics such as room entry and combat formations. They learn how to survive on very little and on how to keep quiet when they need to. They learn how to use things in the environment to their advantage. Snipers learn how to move undetected blend in with theur environments.
Marines also learn how to use computers on the battlefield how to read specialized maps and how to call out coordinates. They learn patience. They will monitor their enemy for days waiting for the most opportune moment to attack. Like I said. Grunts are very intelligent about what they do. Allthough they may not match the intelligience of others sometimes they are not dumb.
Basically what I am saying is Doomguy is probably very intelligent the fact that he follows orders are from bootcamp where you are taught to follow them without question. Allthough because they do whatever they are ordered does not make them brainless or dumb, just disciplined and obedient.