A variety of shaders are simply missing from the game(including almost all of the weapon reflection shaders, and most of the main menu Halo ring reflection shaders, and some covie vehicle shaders)
The network code is horrible...
And there are several more issues, but I don't have time to list them right now since I'm letting my bro borrow my computer for mp while his friend's here, and he'll be back in a few minutes.
If we're talking about netcode and stuff, it can be argued that Battlefield 4 (though I doubt it was a console port) was and still is (though not as much) a pile of crap. The netcode is still atrocious and just until today I haven't been able to get on servers.
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From what I hear, BF4's bad on consoles too, so it's not a matter of being a bad PC port. It's a matter of just being a bad game regardless.
Halo's netcode was actually worse on PC than on Xbox when it was released.
