Now, with the changes and gameplay additions out of the way, it's time to talk about the good stuff - the new monsters, weapon, items and gameplay types.

You also get a slew of new monster types, all but one of which can be seamlessly integrated into the base game through a clever system of equivalency. Save for the Vagary, an enormous 'endgame boss' creature, each monster included in the expansion is equivalent to one of the original monsters. During setup, the Invader player can swap in any number of new monsters by taking their equivalent beasties out of the game. Then, during gameplay, any time the scenario or an Invader card calls for a monster, the Invader chooses whether to place the original creature or its equivalent. The new monsters come with some nasty new special abilities and give the Invader new options for dealing with those pesky marines.

The expansion set includes a new weapon, the Soul Cube, which collects soul tokens that are expended when fired. This ultimate weapon goes one better than even the mighty BFG by instantly killing its target on a hit! New airless terrain, airlocks, sentry bots, mega-health pickups and invisibility round out the pickups and items added to the game. New scenarios are also included, which continue where the five original ones left off and let the marines explore the realm of the Invaders.

Two new gameplay types are possibly my favorite expansion additions. Deathmatch and Capture the Flag allow for up to six players to go head-to-head in a marines-only battle. To facilitate this, the expanion includes three new chainsaw-wielding marine figures and additional equipment bins and order tokens. Deathmatch games are free-for-all battles that end when a player reaches the agreed-upon frag limit. Capture the Flag matches have each team attempting to infiltrate the others base, grab their flag and run it back to their home base to score. There are maps included for each of these game types, and rule changes for weapons and ammo to make them play fast and furious. Most importantly, these modes let an additional two players get their Doom on, which can help when you've got more than four gamers who want to play.