Plot-progression and well anything else, that is. Halo isnt the first game out there to feature super-soldiers and space marines fighting off a alien threat, so what other games seem to have a similar premise or make you think of Halo when you first see it?
My opinion: Xenosaga.
Now, before I get shot with a sniper rifle at point blank and then mercilessly tea-bagged for relating a RPG to a FPS (And even going into this subject), lets break it down like this:
Monolith Soft (the creators of the game) had a series called xenogears which xenosaga heavily borrowed elements, character ideas and even enemies from. very much like Bungie did with Marathon and many of their previous games to Halo.
In the first game of the series, the military presence on the ship is called the 117th Marine Battalion.
Both game series went to only three games (Xeno was supposed to go to 6) the plot progression almost the same way (as in first game drops you right into the story, second reveals twists you would have never expected and the third one wraps it all up)
both feature deadly super-weapons (human made and the like) ranging from the ultimate war machines to Weapons of Universal Destruction.
Both have a evil parasites that absorbs and kills everything in its path (Gnosis)
The ending of the third game in both series for the titular main characters (MC and KOS MOS) XSIII Ending Credits
And which in my infinite boredom and hyper-active imagination I ended writing a full fledged crossover with these two games. sue me.
What are your thoughts? I didnt know where to post this so I put it in General discussion.