Casual Dwarf Fortress Adventure Mode:
-Cover system
-Regenerating health, healing items
-No exploration, go through a linear series of levels with no secrets or sidequests
-Pay for better weapons and armor (not that you'll need it)
-All enemies have been replaced with zombies. Those are popular now, right?
-Now on Android, iOS, PC, PS3, PS4, Xbox 360, XBone, PSP, DS, 3DS, Wii, WiiU, Virtual Console
Hardcore Half-Life:
-Your HEV suit can now break down and needs repairs. Repair parts can be taken from nearby machinery, but some of that machinery controls doors that you need to open or poisonous gas that you need to not breathe
-Enemies can dynamically spawn behind you or around corners even after you thought you'd cleared an area
-All of Black Mesa can be explored as you wish, but you still have to complete your objectives with no guidance but what security guards and scientists you find among the wreckage, on a time limit before the US Military destroys the place
-Use scientific equipment like lasers and prisms, radioactive materials, poisonous gas and the environment to set up traps on par with DF's
"Hardcore" Half-Life:
-Gordon Freeman now wears a fridge for armor, but still no helmet
-Rent-a-cop security guards have been replaced with power-armored marines
-Regenerating health, regenerating energy shields
-Cover system
-Everybody swears every other word. No exceptions
-Everybody smokes
-"RPG ELEMENTS"
-Headshots make enemies' heads explode
-The Xen aliens have been replaced with bipedal aliens with human-like proportions in power armor
-All female characters wear skintight latex hazmat suits or labcoats unbuttoned to their navels
-In addition to grey-brown textures, the entire game is rendered through a low-contrast filter for MAXIMUM REALISM
-Hard difficulty is roughly equivalent to Medium on the original
-Now on Xbox 360, PS3 and PC with absolutely no difference between any of them. A shoddy WiiU port with some tacked-on minigames is coming in a year or two.