The Incredible Adventures of Van Helsing II
is not an expansion, it's a standalone sequel. Further, this sequel promises more than a few added maps and monsters, with a full story that picks up where the last game left off, two new playable classes (including the "Thaumaturge," who specializes in all things magic, and the "Arcane Mechanic," who can create a variety of deadly traps), an extended and improved skill system and a greatly deepened item enhancement system that allows you to break down artifacts into their magical essences and then be combined, altered and applied to items to create new, powerful artifacts.
Multiplayer is also supported, allowing up to eight players to play against each other in PVP mode or up to four players to join forces in Cooperative Mode.
If you're into micromanagement, the new aspect of managing the Resistance may appeal to you; you can micromanage your allied troops, commanding them on how to attack and increasing their weaponry and equipment.
If you're not quite so hands-on, you might appreciate the Chimera (which is obtained during your adventures). Once you claim it as yours, you can send it away into the Ink to hunt for treasure. Then again, if you find yourself in a bind, it might be preferable to have the Chimera available to call it in as support during battle.
Another interesting aspect is the "Hall of Trophies" - special artifacts that affect the world around you, granting such boons as empowering monsters, granting more spellpower to you and your allies or enhancing Katarina's capabilities. Gamers who played Skylanders: Swap Force will be familiar with this game mechanic.
If you're a fan of Action RPGs or Hack and Slash games, like the "goth-noir" feel and steampunk settings or played the original game and are yearning for more, The Incredible Adventures of Van Helsing II might be right up your dark, foreboding alley.