So it's basically just "Gain 5 mana". Nothing special.
edit: And draw a card most likely.
second edit: And attack with your minions twice. Okay. It's a fine card.
No, it's like after this turn ends, your opponent does absolutely nothing on his turn + discards his card draw. If you've ever played against an opponent that ropes out for a single turn, you know you've pretty much won the game after that.
This is an extremely powerful card, the only problem is managing to pull off the quest trigger to get it.
Imagine following: evolved kobold + double arcane giant + time warp: ----> next turn double fireball + frostbolt face for 21 + attack for 18... 39 dmg without giving a chance to respond... Nice to see a "power nine" card coming into HS!
Turn 10 for me: (and still no turn 9 for my opponent): I attack with my two Arcane Giant (your total health -22). If you're still alive, i have now 10 mana for play something in my hand for killing you.