@bigtony @nyanide There's quite a lot wrong, here's how I'd fix it to at least make it an eight or so:
1st & 2nd chapters become skippable, skip straight to chapter 3 route canal, make water hazard shorter and make black mesa east shorter too (and skippable) ravenholm is fine, so is highway 17, sandtraps should be a bit shorter, honestly I'd remove it and just make highway 17 a little longer and go into nova prospekt, remove the ant lion bugbait crap. Nova prospekt is fine besides the antlion crap and with that removed it'd be a better chapter, make the teleport back to city 17 what it used to be, a helicopter ride, more fun and less lame. then the rest of the chapters are mostly fine though i'd remove the human revolutionary NPC's following you. Oh, and remove the "final boss", just have you walk into the top of the tower with breen and it explodes.
Beyond that, there should be general level design improvements (no enemies coming out of one way corridors anymore) and make the guns feel better (sound design + slightly higher damage)
I think all these improvements would make the game closer to an 8.5~/10 for me.