- Counter target noncreature spell.
- Return target permanent to its owner's hand.
- Target creature gets -3/-3 until end of turn.
- Destroy target planeswalker.
Giving a target creature -3/-3 is good, although it doesn't deal with more annoying creatures like Courser of Kruphix and Siege Rhino. But it hits a lot of things and as only half of a whole it's very strong.
The last option to destroy target planeswalker is plenty good. Save your Hero's Downfall for rhino or something else bigger than 3 toughness.
Control decks can definitely main deck a copy of this Command. While 5 mana feels like a lot, this card can do the work of two cards at once, and that's an awesome thing. I see this being very Constructed playable and even good for Commander control suites.