Paying 2 generic mana to draw one card isnt going to feel amazing, but things very quickly snowball from there
The stats aren't worth the cost, but its enter-the-battlefield ability is a game ender: all creatures you control gain trample and +X/+X until end of turn, where X is the number of creatures you control
Additionally, you can run other prison effects like Sphere of Safety and Ghostly Prison and cards that reward you for gaining life like Vito, Thorn of the Dusk Rose
Of course, maybe that was because people were using it to fetch the uber-broken Tolarian Academy
One weakness is that it does not remove the cards
While some creatures like Skyclave Apparition and Witch Enchanter can be used as situational removal, the deck has efficient, low-cost non-creature spells like Path to Exile or Abrade to handle early threats