The addition of the "Jar of Ghosts" and "Stone Staff" items really make this DLC pack shine. Both items literally can mean the difference between a complete loss and bare victory (or a 5 and a 4 skull rating if you are a completionist).
The Stone Staff provides a shot that passes through multiple enemies and a secondary attack that freezes enemies in place. On endless mode, this weapon can mean the difference between holding off 3 Ogres right at the gate and winning or losing 15 rift points. Also, this weapon is great for farming the new "Manaless" bonus-skull condition -included in this DLC- pack on the first mission (+3 skulls on War Mage, +6 skulls on Nightmare).
The Jar of Ghosts provides a passive perk that causes connected shots on you to fear your attacker and an active ability to summon a stationary ghost that casts fear on every enemy that comes in its area of effect. This can be your last line of defense when you have no serious "killboxes" in the early-game. I always have it on my bar for this reason.
On top of the above, you get some of the most interesting bonus levels available to be downloaded. The new maps allow some very creative trap setups, and the new enemies introduced are completely insufferable (and in a game like this, that is a huge plus). Prepare for some hectic and enjoyable gameplay.