Game doesn't start for me either.
Ubuntu 16.04, kernel 4.4.0-7-generic
NVidia GTX960 with 361.28 driver, also tried 352.79
Steam output:
Game update: AppID 291650 "Pillars of Eternity", ProcID 4632, IP 0.0.0.0:0
ERROR: ld.so: object '/home/exp/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/exp/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
Found path: /home/exp/.local/share/Steam/steamapps/common/Pillars of Eternity/PillarsOfEternity
Mono path[0] = '/home/exp/.local/share/Steam/steamapps/common/Pillars of Eternity/PillarsOfEternity_Data/Managed'
Mono path[1] = '/home/exp/.local/share/Steam/steamapps/common/Pillars of Eternity/PillarsOfEternity_Data/Mono'
Mono config path = '/home/exp/.local/share/Steam/steamapps/common/Pillars of Eternity/PillarsOfEternity_Data/Mono/etc'
*** Error in `/home/exp/.local/share/Steam/steamapps/common/Pillars of Eternity/PillarsOfEternity': free(): invalid pointer: 0x0000000002e213a8 ***
Aborted (core dumped)
Game removed: AppID 291650 "Pillars of Eternity", ProcID 4632
Thanks for your help.