I'm sure there are Halo fans out there who are super into the universe but feel like the actual combat of the series is too, I don't know, comical. This mod for ArmA III will fix that for you and then some.
It's looking to take ArmA -- normally a very serious military simulation set in the present day -- and reskin it so that's about Halo's UNSC v Insurrectionists civil war.
It looks pretty good! I especially like the way they got the ODST's drop pods working. Be warned, though, Halo fans; this is a very different shooter experience to Bungie/343's series, so if you're new to it just for this mod, maybe do some tutorials first, so you're not getting your head blown off the second you run into bad guys.