Absolute must is quick reflexes though it is a little buggy with its slow time feature, but if you play at high difficulty then this perk is a must, otherwise elemental protection is pretty clutch vs boss level mages and ancient dragons.
I have every single point in block except that one. I took it initially but re-loaded a save before I got it after playing with it for a while.
The most annoying perk you can get in blocking unless you're into the game slowing to a halt every 10 seconds.
I've got most all the block perks now and can honestly say I don't think the right side is worth it. Even with deadly bash the damage output of a power bash is relatively small. And if I really want to disarm a foe, there's a shout for that. I'd rather stick with the normal bash, which still interrupts a foe, but doesn't do damage. The left side however (plus quick reflexes) is golden! I'd recommend only one point in improved blocking (which gives you 20% better blocking), because the other 4 points only increase by 5% per point. It's much easier to find/enchant gear to give fortify block gains than spend those 4 perk points.
It's not about the damage but about the stagger. And even then the power is quite okay. I've killed dragons using only power bashes.