Okay, I'll bite!
My idea of a combat revolver begins with a harder-hitting cartridge than .38 Special, i.e. .357 Magnum.
Add a bobbed or semi-bobbed hammer and a trigger job.
Perhaps add a front nightsight. Rear sight is likely fixed.
Barrel length is 21/2 or 3 inches.
Maybe hardchromed or black matte.
Grips should be concealable but manageable; I prefer wood over rubber.
Six shots minimum. Perhaps the charge holes are chamfered.
Likely carried in an IWB holster, with a speed loader or speed strip(s).
Revolvers that come to mind are my S&W Model 19 (set up as above) or a Ruger SP, GP, or Speed Six series.
What have I left out?
Oh yeah -- How is it better than a semiauto? I'm not sure it is, but a few ideas: draw and fire (no safeties to swipe); not ammo sensitive; may stand neglect (not abuse!) for longer periods, i.e. lack of lubrication, presence pocket or holster lint, etc.