Using triggers = closest most of us will have to feeling badass and using a real gun
For every game that has the feel of "shooting" gameplay mechanics, I would want to use the right trigger for shooting (primary), left for special or secondary functions like grenades or aim (like in CoD and every other shoot than Halo and HL). I was pretty skeptical about Halo: Reach's right bumper for melee but it feels better than B button because I can now aim AND melee at the same time. If a game even switches up any of these functions, I will most of the time not even play a game because of it unless it seems reasonable.