One thing that can really give it to you in the game is when you have to reload in the middle of getting clawed or beaten on by wrenches. The rub is that you reload basically the same whether you are being attacked or not. I suspect if a demon from hell was clawing me to death, I might move a wee-bit faster.
Two interesting ways to handle this:
1) Show a faster reload animation signifying the marine trying to get things done faster. However, this would be coupled with a percent chance of dropping each portion of the reload. This would animate as the player dropping some shells. So you might only get 4 shells reloaded but use eight in doing so.
2) Allow a button that does a fast reload. This reload would take say 75% of the time a normal reload takes, but would only insert half the amount of reloaded ammunition. In the short term (if you only have to do this once), you might be better off, but if you are in a prolonged fire fight the longer reload might be better. This gives a new tactical (right word?) decision to the player that can make things interesting.
Just some thoughts. :)