I have the minimum requirements. By default, the game ran at an appalling speed. I had to search online to find tweaks for the configuration, just to get the game to run at a playable speed. Even after all of the tweaks, there is still considerable slowdown when near water and the general performance is lacklustre. Aside from the performance issue, which admittedly will be less of an issue for people with higher powered machines, inexplicably the demo ran fine for me and suffered no debilitating performance problems.
Stability is a problem, though.
While every other Loki title I've tried has been solid as a rock, Heretic 2, even with the latest patch, crashed often. And not just segfaults that dump you back to your desktop and leave a bunch of messages to help debugging. These were total showstoppers that took the window manager with it. One even neccesitated a reboot due to a total lockup of the system. Reboots in Linux are for adding new hardware or upgrading the kernel.