Ok, I'm new here, blah blah etc. Hi! :-)

I am always looking for new ways to improve relisim in my games without increasing the rules or required book keeping. For example the your turn/my turn tennis match or most RPG's combat has always bugged me. Giving multiple attacks requires an extra level of complexity My solution was to say that if you didn't pass your initiative rool, you couldn't attack that round. A bit more random perhaps but it was interesting and fun and over the course of a combat those who should get more attacks got them. Anyway...

My latest concept along these lines is to replace dice with a hand of standard playing cards. The number of cards is determined by the characters combat training, say between 3 and 7? One card is played by everyone at the start of the round for initiative and the rest are for your attack and defence actions throughout the round, one per skill use. At the moment I'm thinking that skills will be rated 1-10 and you can play any card up to that value when you use that skill, while one equal or higher is needed to counter it. (eg, you have a sword skill of 8 you play a 6 card to attack with your sword so your target need to play a card 6 or higher to defend. If he has no defencive skill 6 or higher then he has no option to defend)

There are many advantages to this system,
1- The size of the hand is a simple (effortless) way of giving greater tactial options to the players of characters who have the training or experience to be using tactics themselves in a life or death situation.
2- The quality of hand you are dealt give a clear indication of the situation your character is in at the start of the round.
3- Tactical options are plentiful, do you use your higher cards for initiative, attack, save them for after you feint with a lower card or save them for defence?
4- Immediate disadvantes can be easily represented. (eg discard a card at random when your opponent get's a successful hit)
5- Your character's position in the combat (how well he is doing) is tracked turn-to-turn in the quality of the cards in his hand. If you contune to play all your good cards, either in attack or defence, then you are over-reaching yourself and you will be left with a hand of rubbish cards to carry from turn to turn. Whereas you can choose to hold back a couple good cards to surprise your opponent with a couple turns later.

Anyway, I suspect I've written more than enough for now. Although there is of course more. What do you think? Do you see any problems with this? Any suggestions for changes and improvements? I know there are plenty of other card-based RPGs out there although I have somehow managed to avoid all of them so any gems of wisdom from those whould be much apprieciated.

On the face of it, I see nothing wrong with the system you've presented here.  It seems to give a lot of advantage to skilled characters over unskilled ones (unskilled characters get fewer cards, and can't use their cards as effectively) which might be a problem if that's not the feel you want to go for.  You need to clarify the rules for carrying cards from turn to turn.  At the moment I can see no advantage to holding on to good cards, since you're either going to hit them, or they're going to use one of their good cards to block you. 

I think you need to clarify the turn structure of your game, too.  Who plays cards when? I'm unclear on exactly how this works, whether you both play all your cards until you run out (in which case having more cards than your opponent seems like an almost assured victory) or if you get re-dealt before you run out of cards.

One advantage of using playing cards that you're not exploiting right now is that they contain a great deal more information than dice.  I'd love to see your system include the suit of the card in some way, as an added tactical twist.  Maybe some suits are more efficient at blocking, while others are more efficient at attacking? Maybe some suits you get to play face down, and the opponent has to gamble on what card to play against it? Maybe there's a suit that does extra damage on a hit?  Face cards also give you a great opportunity for adding "special moves" to the game. Trips, dodges, disarming, and bullrushes could all be represented with these cards, which would be exciting for me.

Lastly, I'm troubled that you include "realism" as a design goal.  It's not bad in of itself, but I think you'll find that it's a goal that almost never helps produce a great game.  The problem with realism is that it's never the same for any two people.  None of us have extensive experience fighting for our lives with medival weaponry, so none of us can really say.  Even if we did, there's no way to say that a "realistic" game is any better than a non-realistic one for your group. A better design goal, I think, for what you're trying to do, is to think about what factors make combat fun and exciting for your group, and work towards that.  If you like a system that rewards skilled combatants, design something like that.  If you like a system that's very random, design that.  If you like tactical combat (and it seems like you do) concentrate on making a fun tactical card game, rather than a realistic combat simulator. 

Good luck with your game!