I fought one of the giants that like to hang down by the beach. Had that bastard about 75% dead before getting wasted.
Don't sleep on fully charged R2 attacks and jumping R2 attacks - these do WAY more poise damage than R1's and most L2's
Every enemy has an invisible poise bar that decreases with consistent attacks (wait too long between attacks and that "bar" resets)
When you fully deplete that bar the enemy will become stunned and open to a critical attack
2 or 3 charged R2's with the Claymore will be enough to make those giants crumble to their knees - at that point run up to their face and press R1 while holding forward to do the critical attack
It's generally the best way to fight most "giant" enemies