compared to 2.2 its not that RF is broken in 2.3 its just been dumbed down to the point of uslessness, most of my battles do not involve reaction fire from my units or from the aliens. Basically what happens is that for a reaction fire to occur you require vision of the enemy for the time units needed to fire your designated RF shot.
For example you set your heavy MG on full auto (25 TUs) reaction fire mode. Then an alien walks right around the corner (2 TUs for the 1 step you seen him) fires at you with a pistole (8 TUs) then ducks away around the corner again. Basically you seen the alien for 10 TUs and thats not enough to trigger the requirement of 25TUs for full auto RF. The alien can keep ducking in and out from a corner and no one in your party will get a shot off unless they have really low RF TUs (basically pistole level or snap shots). For this reason you see aliens walk right infront of you, shake his ass, walk past you and your units just stand there doing nothing. So currently for reaction fire to be of any use you basically have to choose the weapon and fire setting with the lowest TU cost.
This was changed due to some one complaining that he gets RFed upon every step by the same alien unit. Although now I dont see Aliens RF at all. This basically kills the reaction fire mechanism and makes it pointless wasting time units in saving for reaction fire for your own units as well. Perhaps a mid way would be for units to fire at any interval between his required RF TU cost and then not be able to fire again untill the next interval, but its all up to the devs
For more info read this thread
http://ufoai.ninex.info/forum/index.php?topic=4302.0