Decided to play through it again and get the little purple hat achievement, great time all around. It wasn't much of a challenge I guess, more just a minor annoyance to keep track of. Source is just godlike to me man, shooting a headcrab with a shotgun or blowing up a barnacle with a satchel never gets boring. To list a couple nitpicks though, the game crashed a couple of times (especially in Interloper) which wasn't a big deal since I was quicksaving a ton for the challenge, but having to let it load all the way back up was annoying. Sometimes the plugs in Xen would just not plug into the sockets too, effectively softlocking me. Most annoying of all, I'm not sure why they added the pizza achievement (which is just a rehash of the Hat achievement) that makes you carry a prop through all the most annoying sections of the game again. It's a fun little secret ending, but I think the pizza should've been hidden somewhere a lot closer to the Nihilanth. Those all aren't really big deals though! The level design improves upon Half Life's strong foundation really well and Xen is much, much improved over the original. What was an unfortunate ending to a great game is now just... the great ending to a great game. I still love both, hell, I'm playing through Sven Co-op with some friends right now, but I'd probably pop in Black Mesa on any given day