A while back I found using the ia32-libs package was a way to get Dungeon Defenders going on 64-bit Linux, but that package went away. Here's the process I went through to get Dungeon Defenders working on Xubuntu 14.04.
Graphics SetupFirst in general: install graphics drivers. For nVidia this is basically:
apt-get install nvidia-currentnvidia-xconfig
For AMD the process is a little more fraught with danger, I found this process works well with 14.04 though:
apt-get install fglrx-updates fglrx-amdcccle-updates
aticonfig --initial
Then reboot. After, if using AMD, run amdcccle and set the "tear free" option to enabled.
Game SetupSince ia32-libs is deprecated, I went through and manually found all the packages. Here's the summary that should hopefully include everything needed to run the game:
apt-get install libglu1-mesa:i386 lib32stdc++6 \ libxext6:i386 libasound2:i386 libpulse0:i386 \ libxcursor1:i386 libxinerama1:i386 libxi6:i386 \ libxrandr2:i386 libxss1:i386 libxxf86vm1:i386
Then, before you run DD for the first time, edit the file DefaultDunDef.ini in UDKGame/Config/ and remove "_Valentines2013" from the GameplayLevel parameters, so that they only say "LobbyLevel.UDK". This will prevent the bug when you start the game it goes straight back to the menu.
(After using it as a test application for a fresh machine, I want to go back and play the game from a clean start. After the débâcle that is Dungeon Defenders Eternity, the original game feels much more...fun :(. )