^It's actually been quite a while since I played the original. I think the last time I had it installed I didn't get much past 'On a Rail'. The game sort of grinds to a halt there. Thankfully I think the mod greatly cuts back on that section of the game.
Now that I think about it, I think I've only ever made it all the way to Xen twice, not counting 'Opposing Force' & 'Blue Shift'. It's actually quite a long game, even at the time and most especially by modern standards.