kalirion: Half-Life: Opposing Force Pretty good expansion, nice new aliens to replace the marines as the most troublesome enemies.
That was a good expansion. It's been a decade but I remember enjoying opposing frce more than the original. I still have the install discs for half-life and opposing force. I did lend out my official game and key so it's been registered on steam but hey I can still install it drm-free for single player.
I finished off Doom II : Hell on Earth. More challenging than Ultimate Doom, but the level design is better in Ultimate Doom. That said, the double shotgun alone makes the game worthwhile and a solid 9/10. I even (accidentally) found the secret exit to the bonus Wolfesntein level which was cool.