Block affect both block chance and block damage reduction. This makes block almost negligible at early and mid game then suddenly becomes more and more important later, and make players frustrating when fighting high-end monsters which always have over 750 block.
A simple solution: make block only affect block chance (=0.1% per block, as ever) . Change the damage reduction to a fixed number (for example, 40%) and increase it with power and block(flat increase. Block is more effective than power), and gear attributes(percentage increase based on actual damage blocked).
Solid give multipler to reduced damage(1% per level), not overall damage reduction percentage.
Example of formula above:
attack with 50000 damage blocked by an enemy with 750 block and 4000 power:
It should take (20000 + 750*5(block effect) + 4000(power effect) =27750) less damage compared to 37500 less damage with current formula.
If an enemy with 150 block and 100 power is hit by 50000 dmg attack and successfully blocked, it should take 20000+750+100=20850 less damage, compared to 7500 less damage.
Block damage reduction is still capped at 80%.
P.S. Make block able to prevent spell damage (25% base reduction) should be a good idea too.