Mods usually extend the life of a game by tenfold. Just look at Skyrim. The game came out three years ago and new content is being generated by the community on a daily basis. This means you can jump in and find hundreds of hours of fun even after you finish the in-game content.
With Metal Gear Solid: Ground Zeroes now on PC, modders have been busy trying to add interesting riffs on play. The most intriguing I've seen so far is no doubt this mod which puts the player in Snake's shoes by changing it from a third person game to a first person one.
You can check out footage of the mod from Youtuber BenBlatcher below:
This is actually a really admirable effort as it was no doubt a difficult mod to get working properly. Games that are designed in third person often need a lot of re-tweaking to work in the first, so kudos to the creator. There are several bugs such as object disappearing if you get too close to them, but for a homebrewed effort, this is impressive work.