As I'm writing this I have just gotten done playing Last Night on Earth with my son. We play the core game a lot, but this was our first time playing this expansion. I have to say, it really added something to the game for me.
If you haven't played Last Night on Earth before, it's billed as a B-movie zombie board game, and it hits that point pretty spot on. Play is for 2 to 6 players, divided into two teams. One side plays the zombies, the other plays as the heroes. Each side takes a turn until the win conditions are met.
Because of the modular nature of the game those win conditions change, as do the heroes, and the board itself. This adds a little variety to the game that we find really fun.
Anyways, I wanted to comment on this expansion in particular because it added a couple of compelling new rules to the game. First, heroes and zombies now gain experience as they hurt the enemy. This really encourages more aggressive play, and adds just one more level of variety to the game. Now the heroes themselves are different each time you play.
Second is fire. The way it's handled in this game isn't exactly new. It works much like it does in games like Flash Point (though maybe not as well since fire isn't the true focus here); each round you roll for each space that is occupied by fir. roll high enough and it expands to a random adjacent square.
This was huge fun for me, maybe just because of the way it worked out in my game, but it added an element of randomness that was dangerous to everyone on the board. At one point one of my heroes tossed gasoline into a building that my son was hiding zombies in (I needed to kill them for the win condition and my heroes couldn't get in), and then set it alight with a flare gun. Many of the zombies survived the initial attack and came pouring out of the building into my hero's space, followed immediately thereafter by the fire which expanded to engulf them all. It was all she could do to get away, and I had to spend the rest of the game with her hiding just to keep her from turning into a zombie too.
And that's why I love it. Why I love random elements in games in general. It's why I use fudge dice in my campaign creation system. Randomness creates emergent gameplay. It creates stories, and forces existing ones to bend in unforeseen ways.
If you haven't played Last Night on Earth or any of its expansions I recommend them. I don't have them all (yet), but the ones I do have proved to be great fun.
If you never use randomness in your story creation I recommend that as well. There's nothing wrong with a well plotted story, but by adding in a random element you allow everyone to be surprised, even yourself. It takes away a bit of predictability and encourages creativity.