Metal Gear is copyright, you can see the copyright symbol on most of the boxes.

Metal_Gear_cover.jpg

Trademark is more of a process, design or expression meaning it is closer related to a patent than a copyright and from my own limited understanding, has more to do with name recognition and commercial usage.

This is literally a remake of the original game so this is definitely infringement on copyright but it is up to the copyright holder to do anything about it. It is just nice to see a company being cool about letting fans work on it. Usually making fan sequels is more of an issue because if the copyright holder ends up using an idea from a well known enough fan sequel, it is possible the fans could try to sue for infringement, though the fan will most likely lose the case it is still easier for the copyright holder to kill the problem early before it gets into legal issues, which is why things like Chrono Trigger Crimson Echoes got a cease and desist letter.