Now is a great time to pick up some DLC's! From June 26th through July 10th these three DLC's are 50% off. Each of these DLC's add an additional world that you can travel to via The Gate. Each has its own distinct environment and monsters.
Delve into dark, damp, mysterious caves in The Caverns of Grimlock where Driders, Mothmen, and Redcaps make their home. Maybe you'll stumble upon a pack of filthy Troglodytes, or have a Choker pop out of the dark and grab you, or encounter Grimlocks that worship and do the bidding of the horrible Mind Flayer.
Fight a myriad of demons and devils, like Dretches, Bone Devils, Imps, or Chain Devils, in the hellish landscape that is The Abysmal Furnaces. Maybe you'll run into the pig-like Nalfeshnee, or the terrible Marilith with her snake-like body and six arms, or even the fearsome Balor with his fiery whip.
Or run around amongst beaches and palm trees battling many aquatic creatures like Kuo-Toa, Bullywugs, and Sahuagin in The Swampy Isles. Maybe you'll encounter sharks or Drowned Men at a shipwreck, a Swamp Hag in her lair, or be devoured and spit back up by a Froghemoth.
All of these DLC's contain anywhere between 28 and 44 new monsters to battle. Additionally, they each add new weapons and armor, plus abilities and skills. There really is quite a bit of content included with each to add variety and challenge to the game. Don't delay ... the sale won't last forever.
Note that to load any DLC you must have unlocked the main game.