I think 1.9 combat update is bad, so, here suggestion how to improve it.
Player can attacks with sword or axe by pressing right mouse button. 75% of damage deals to sword, 25% to health with armor. Also effect and sound of parrying would be nice. However, player can't hold parrying always. After pressing right moust button, player'll be able to parry like for 1-2 seconds.
Shield, unlike parrying, can be ready always, but will slow down player. Shield will take all damage, however, will take additional by axe's full charge attack (read belw)
3. Pre-attack animation
When somebody attack with sword or axe without full charge, they do pre-attack animation to warn enemy that they must block or parry.
4. Sweep improvement and shield crushing
Player with sword full-charge attack must hold shift and then attack to prevent accidental team-kill. Also, sweeps really should be sweeps, dealing damage only to target and it's closest allies, not around.
Shield crushing can be done by axe full charge attack. Player hold shift and instead dealing crit, he will deal massive damage to shield or will ignore sword's parrying. But failing to deal full charge attack on parrying or shielding enemy will result in low-damage and knockback of attacker.
5. Overhead attack
Jumping and attacking with full charge at same time will result in overhead attack, failing overhead attack (blocked, parried or missed) will result in short (let's say 2 seconds) slow II and additonal knockback on defender's attack (if parried or blocked).
Players able to dodge (dashing left, right, forward and backward) attacks. Dodging took half of ham. Nuff said.
I think to improve combat we need to, instead of adding more offensive features, directly nerf the fundamental way it works in this game. I loathe 1.9 mechanics because Minecraft is not a sound game in this respect. Everyone prances around jumping constantly, you get stuck on blocks and ledges, hitboxes are atrocious... the game was not built for PVP, and thus the PVP community spawned from it is more about learning how to abuse the system itself than strategically sparring. I preffered it when everything was just a spam-click fest, at least then I might win a fight with the op-diamond nutcase using no-fire resource packs and spinning his screen 360 degrees.