With the Interrupt, a very important thing is to know when to use it though. If properly used it can make the fight a lot more interesting, but if the user is too 'trigger-happy' when it comes to the Interrupt it can give the opponent the feeling he/she is never allowed to make any move because everything is always cut short.
Another thing that has to do with this is the difference in speed between the fighters. The idea 'one action per turn' works when the fighters are about the same, but if you have for example a heavily armoured fighter with a two-handed weapon fighting against an assassin-like fighter with little to no armour and only two daggers, it means that the assassin is put at a disadvantage because his speed advantage is decreased. Yes, the assassin could just use a faster kind of move, but if he can only use one move before the 'tank' fighter does something in return it means that even though the assassin's move may be faster, he would only be able to use one while his speed might be enough to execute two actions before the tank can react (wouldn't find it that hard to believe some assassin or monk could hit a tank twice before said tank has the opportunity to counter). Of course, the 'one action per turn' system is not bad, since it prevents one person from beating his/her opponent up in one go, but it's not perfect if you look at all the more specific scenarios.
And the obvious thing, realism is important. Even though you are in a fantasy based world, it doesn't mean things don't work along certain rules that must be followed, combat being no exception. Everybody likely already knows this, but using a move that makes little sense (for example, the tank from the previous point swings his/her two-handed weapon, then in mid swing suddenly changes its direction at a 90 degree angle without losing any speed or power behind the attack) will make the opponent feel like the fight is not very realistic any more, and might even react with another nonsense move. I just want to point out, think about your actions and whether they're actually realistic before using them.