Great addition!

Really good expansion. Adds more to an already great game.

King of Tokyo Power Up
The core game is such a blast I felt this expansion pack a 'must buy'. Our gaming group love KoT but we all feel the power up pack changes the dynamics of the core game too drastically, our games tend to last an awful lot shorter using this pack. We have played most of our games with 4-6 players.
Now, it certainly does what it says on the box, 'Power Up', all characters have a bundle of unique power cards that are akin to the base set. These cards are, on the whole, very powerful and there's often an amount of luck as to who gets what and when, knocking other players out very quickly. We've since not used this additional set for our last couple of sessions, with the whole group voting to just use the core set (5 players in both sessions).
To add an extra dimension to the core set, this is a fine purchase, we, as a group, don't feel it's a necessary purchase though.
Happy gaming! C

The evolution cards are really good.

The Power Up! addon is a really nice addition to King of Tokyo making each monster feel unique. Before all the monsters were exactly the same and who you picked really didn't change too much.
Now though each monster has different powerups, The King for example has alot of buffs to get him into Tokyo and power him up while he's there. While the Kraken is all about taking less damage.
It makes rolling hearts to get stronger a much better option. What was usually everyone trying to get as much energy as possible turned into trying to get a nice mix of things both to power up and to get the bonus effects of other rolls.
If you've got King of Tokyo it's well worth the money for this expansion.