A few things which need changing:
1. Don't have defensive "set-plays" assigned to directional buttons, because when moving players around, you can inadvertantly move your entire defense.
2. With attacking set plays, once you have called the set play, the running lines of the players are set, then all you need to do is choose who it gets passed to (buttons 1-4 or whatever) and then you are controlling the receiver before he gets the ball. This means that you can aim at gaps to get through. The outside half should be controlled by the CPU unless it is a fly-half "running play".
3. There should be a choice of defensive tactics such as Rush defence, drift defence, spread defence, and whatever else you want. This means that certain plays would work better against certain defense types. For example, a switch may work well against a drift defense as you can attack the weaker inside shoulder.
4. Here's a good one. How annoying was it in Rugby 2005 when you would run diagonally with your fly half wanting your centre to straighten up and hit the gap, and he would run away from you? What should happen is you hold the "pass right" button and flick the right analogue stick along the line you want your "right hand man" to run. Hold "left pass" button for your left hand player. Either this or create some inventive AI that doesn't just keep a set distance from the ball-carrier.
5. Kicking out of hand is made quicker. As well as the kicks being longer. Perphaps L1 or R1 modifiers could be used for kicking high/low so you could drill a kick into the corner into the wind, etc. Rather like in Pro Evo Soccer.
6. Not have such long motion-capture sequences. For example, their is that wierd animation you get sometimes when you sort of get wrestled to the ground by the defender. This animation kicks in really early and you cannot pass the ball away even if you're 3 on 1 against the full-back. The same goes for the sidestep animation. It should be lightning-quick for some players, and slower for others. In Rugby 2005 it was the exact same animation for all players.
7. Outside half runs onto the ball when passing off rucks/mauls.
8. Forwards are made less energetic and move in a pack less. They get up from rucks too quickly and are at the next ruck too quickly. This affects things like returning punt kicks. Watch international rugby and you'll see the play get very broken after a clearance punt which doesn't make touch. The full back has plenty of space to run into and there is lots of space between players so you can take players on 1 by one rather than trying to run around an entire pack of forwards.
9. You should be able to slip a tackle without slowing down. It annoyed me so much in Rugby 2005 when you would slip the tackle from the centre, say, only to be munched by another player because you were slowed down so much getting out of the tackle. You should sometimes be able to bust through at full-pelt. This is also to do with the overcrowding caused by the over-energetic players. In real rugby, not every player follows the ball and tries to get to every ruck. You have to take some time out sometimes.
10. Ability to exploit mismatches in defense. In gameplay terms, if you are controlling say, Daniel Carter, and you see two fat-boys in the defensive line, they should be pretty easy to run between, but if you run right at them, you are in the ****. Similarly, a forward with the ball should be able to bundle over a small back when he is at full pace.
11. Players should not be able to change direction so quickly. That thing you can do in defense in Rugby 2005 where you sprint along the line until 9 passes the ball then you turn upfield and bosh the outside half is just silly.
12. A button in defence to be able to move around but face the ball carrier. This is absolutely essential. If you had to face the same direction you wanted to move when defending in real life, it'd be hilarious. In a game, it's not funny. It's irritating. You find yourself running away from the ball-carrier and then turning back to try and face him to tackle him. Or letting him come past you and diving in from behind.
13. The AI should have some tactical nouse. They should try and use real-life tactics to win matches and sustain pressure. They should bring the defense in with some tight play, then spread it around to the backs. That's how Wales won the 2005 6 Nations Grand Slam. And most of their players aren't that good. In Rugby 2005, the CPU gives up the ball too easily. I often can play a game with 80% possesion on Hard Mode. That is just silly.
and finally...
14. Offloads. There was a time when it was against the laws of the game to offload from a tackle. Thank the Lord that rule was changed. What would the current All Blacks side be like if they were unable to offload? When they make those 70-yard gains without changing phase, they will offload so so often. I counted 7 in a row against England when that guy dropped the ball when he was over the line. Good tackle by Cohen on Umaga though!
That's enough for you to think about.
If HB came to me asking for a game design, it would be the absolute dog's ********, I guarantee it.