Dark Messiah of Might and Magic, and a lot of other early Source games will just outright crash.

Crysis Wars, Word '03, the Saboteur are all in a similar boat.

They're not address aware, meaning they overallocate at launch, and Windows handling of 32bit compatibility is dead end code that hasn't been worked on in decades. These are 64bit executables, with 32bit memory mapping inside them.