I could personally only see a fully iterated melee combat system working if game had specific melee classes, classes that you could see logically surviving the charge into a gun battle. Sure, you could go with the whole, overdone (IMO) space ninja route, but I think it would be far more interesting if the melee classes were more than a person doing flips while waving a katana around.
Something like an alien with natural weapons and armor; like the Rachni; would be a very unique kit to use, or even a human in a suit of heavy armor specifically designed to crush things in close combat:
Having melee as an optional auxiliary, should the firefight get too close for optimal gunplay, is fine but a solely melee focused class shouldn't be a viable option unless one was going to go with one that was specifically designed from the ground up with melee combat in mind, and would actually stand a realistic chance at engaging enemies equipped with guns.
I personally like to see my melee users a bit more 'grounded' as it were, I'm rather sick of the whole: 'ninja with a sword taking out an entire platoon of soldiers equipped with assault rifles' anime/rule of cool nonsense that is prevalent in most mainstream media. To me, it makes way more sense to see a Rachni or Armored Mec suit closing the distance and slaughtering a group of solders in melee combat, than it does for a random dude in space pajamas with a flimsy katana going in and wiping out everyone.