Heretic 2 was crap on the PC. Too much virtual memory thrashing, especially when you hit alt+tab to go back to your browser to find some decent servers to play on. *grind*...*grind* (watch the screen redraw line by line)...IE stops responding...*grind*...reload IE...*grind*...switch back to heretic II screen...*grind*...windows crashes.
Actually, it's the same for all Windows games no matter how much memory you have installed. Windows seems to stupidly allocate all memory for any running task. Wow, what fun - not.