I finally got around to playing Half-Life: Decay. It's not particularly great or noteworthy, but just something I wanted to play at least once. It was a PS2 exclusive co-op HL game, and was fan ported as a HL mod to PC. You play as two female scientists, one of which is the lady from the HL training tutorial. It begins by you preparing the specimen for the experiment that Freeman would then perform triggering the Resonance Cascade event. It continues the Gearbox HL expansion motif of showing you alternative perspectives during the Black Mesa incident, which I always enjoyed. The level design and enemy placements aren't great though. It's a lot of enemies spawning in. The co-op puzzles are interesting though -- the only real highlight unfortunately. Unlike actual HL or its expansions though, you don't always start the next level where the last one ended, which doesn't make it feel like as connected. Maybe a PS2 limitation or just a design choice, I don't know.