You can go after them to make your creatures stronger and put some pressure on them
It's not widely played anymore as other, better options have been used, but being able to target both creatures and planeswalkers helps to get rid of two potential problematic permanents, giving it versatility that other, similar cards don't have
That said, this isnt the first time weve seen a Black commander with an ability ripe for exploitation
A cards rarity is almost irrelevant
The need to play it immediately represents the fact that Anakin needed to change quickly if he were to survive his injuries, and making the creature an artifact in addition to its other types represents how Darth Vader is more machine than man. #16
But Emrakul, the Promised End is easier to cast, not banned in Commander, and can sit at the top of Eldrazi ramp strategies, reanimator strategies, and even Birthing Pod setups