HL: When you first get the rocket launcher/bazooka
BS: Didnt really like anything
OP4: Boot Camp
HL2: The lighthouse in Highway 17
EP1: When you fight the zombies in the dark waiting for the elevator (on hard its my least favorite)
EP2: When you first get to the base in White Forest.
Grenade-Catapult puzzle from Ep2. I lol’d.
HL1: When in Unforeseen Consequences the part you press the elevator button to make the elevator fall, a scientist says “Ah, Freeman.” before falling to his death.
HLBS: At the beginning when you see Freeman in the tram.
HL2: Running over a Combine with the jeep.
HL1 : Unforseen Consequences
HL2 : The chapter with the canals (forgot the name)
Ep1 : Don’t know actually
Ep2 : When the Vortigaunts are bringing Alyx back to life and you have to kill off the antlions
OP4 : the final boss at the end.
Half-Life: Emerging from the pipe in Surface Tension.
Blue Shift: When the train car thing crashes near the start.
Opposing Force: The plane crash at the start.
Half-Life 2: Meeting Alyx and all of the Citadel.
Episode 1: Dog throwing the car into the Citadel, the train crash at the end.
Episode 2: The final scene, the bridge breaking and the Dog vs Strider fight.
I always loved the part when i got the hornet gun. I always made a save game so i can start from there.
There was one bit on Surface Tension (I think) where I teamed up with a security guard. He happened to die next to one of the bounce pads and ended up eternally bouncing up and down.
Half-Life: Firing the rocket in the chapter “On a rail”, and walking along the cliffside in the chapter “Surface tension”.
Opposing Force: Sitting in the osprey at the beginning, that was pretty awesome.
Blue Shift: The whole ending when you are waiting for the portal opening so you can go through it at last, and then escaping from Black Mesa. 
Half-Life 2: The beginning and walking under the bridge in the chapter “Highway 17”.
Half-Life 2 Episode 1: Riding out of city 17 at the end. Great fireworks! lol
Half-Life 2 Episode 2: The whole chapter “Freeman pontifex”, and arriving at White forest, where Dog is knocking down the strider. 
Portal: Getting into the hall where GLaDOS is hanging around.
Lost Coast: Inside the church. Nice building. :3
HL: Basically everything, as it was so new for me with the FPS genre, and the graphics were astonishing. But the resonance cascade, surface tension and Blast pit probably were my favourites.
OP4: Oh, long time since i’ve played it now, but I remember the zombie in the beginning at the hospital, just suddenly rising up and kick’d the ass out of the scientist examinating him. that just freaked me out. Oh and I enjoyed Race X and all the cool weapons you got to posses.
BS: hehe, same goes for this game as with OP4 don’t really remember all the details anymore, but I remember it was cool seeing Gordon Freeman from an outside perspective! First on the train-ride, then in the video surveillance room on the screen.
HL2: ahh… Of course the astonishing graphics, the gravity gun, all the zombie-raping in Ravenholm, climbing around using various props and of course the citadel. Well, the whole game was awesome.
EP1: The car-rollercoaster, and also the strider fight at the very end!
EP2: It was just pure ownage!!! The whole thing, but I remember mostly the cool beginning when the bridge collapses, and the Catapult-puzzle, it was just so Freeman-ish, the battle of white forest, saying goodbye to Lamar and the huge WHOA-ending!
…
I’m probably the only one that likes the beginning of HL2 where all the people are milling about in the train station. Then you have this guy rambling, “…they’re always departing but they never arrive… and the ones that do arrive… they never leave… you never see them go; they’re always full… no one ever gets on but they’re always… they’re always departing but they never arrive…”
To me, when I first played HL2, I was like…What…The…FUCK is going on here?! With Breen propagandizing from multiple viewscreens… Then you get to the CP who is abusing that one citizen by the luggage cart…and all the way up until you meet Barney (the CP closing the peep-hatch in that door was awesome)… then, of course, there’s opening the door into the courtyard. D: :awesome: It’s so beautiful! :’(
HL1: Half Life was my first PC game, and I love it all. But my favorite level is Lambda Core.
HL2: When I take pulse rifle first time. City 17, Combine’s domination, Striders, gravity gun… Half Life 2 is full of WIN.
Ep1: The Citadel Core and battle with a combine gunship.
Ep2: Forest. I just leave a car and go walking. And distant hunters screaming. And hunters ofcourse. And Advisors.
HL series was awesome! everything was perfect but my faves r:
HL1: “Surface tension” the part when u coming out of the pipe to a cliff and see the jet fighters
it was awesome!
i cant wait to see it in BMS
HL1BS:Xen was cool and the ending when u hear the soldiers takeing Gordon to the trash compactor “What r u waiting for!? lets kill him now!” “Uhhh what about the body?” “Body? What body?” chuckle
HL1OPFOR:That gianbt trash worm. and the plane crash at the beggining.
HL2: “We dont go to ravenholm” “Sandtraps” i think when i was under the bridge.
and “Follow freeman”
HL2/1: bridge crash and the train with the exploding citadel.
HL2/2: white forest rebels were awesome!
i cant wait till episode 3!
can’t hardly remember the standouts of HL1.
but that’s why i’m here, saving myself to replay it for black mesa.
HL2: so many great moments, but greatest is after defeating the copter before black mesa east, the feeling of total holocaust. a beautiful holocaust & view.
the silence after the boom, and then finding the path and seeing those familiar faces.
never much was a fan of being overpowered, so the blue gravgun didn’t do it for me.
episode 1: lowlife: perfectly titled chapter. the feeling of the rest of the city being in a state of total decrepitation while you and alyx are on subterranean pitch black struggles trying to get back to the center of the fray. then finally the grey snow and kleiners message.
episode 2: silly but likeable griggs & sheckley, and then to the surface n the view of the bridge with all the combine moving their pieces and the speaker voice. very epic.
the ending is terrific too.
I didn’t really care for the characters of Griggs and Sheckley. Too Laurel and Hardy/Abbot and Costello if you ask me. They had some good lines (“I got ten!” “We all got ten! There’s hundreds!”), but to me, they’re more annoying than anything…and seem out of place in a Half Life game.
But, ehn. To each their own.
I thought Griggs and Sheckley were awesome. 
It made a slightly repetitive battle seem fun and exciting.
yeah, more personality than the average resistance fighter. the “seems like something the vorts would say”-lines truly made me lol.
i thought about the favorite HL1 moment. gotta be the first malfunctioning obstacle and first headcrab. the inception to magic and brilliance.
After thinking over Half Life, I managed to narrow down my two favorite chapters from it, and why I loved 'em.
I thought we should all try!
It doesn’t need to be two, by the way.
Here were mine, with 1 being the best
Surface Tension
First off, let me get this out.
This is the longest damn’ level in the entire game. I don’t care if I’m wrong, to me it is.
First you start off seemingly still early in the game, finally getting to the surface, the one place you need to be, thankful to be out of the underground hellhole that is Black Mesa, only to meet up with a heli going berserk on a dam.
After going through soldier after soldier, mine after mine, alien after alien, three tanks, an osprey, three alien grunts, ANOTHER HELI, a tentacle seemingly out of nowhere, a shark, a pit full of trip mines and suicidal headcrabs ready to leap at you straight through the lasers, ready to blow the entire damn Black Mesa facility up, scaling a huge fucking cliff, ANOTHER HELI, and too many soldiers to count, you GO BACK UNDERGROUND (At which point I yelled out quite loudly: “OH YOU HAVE TO BE SHITTING ME”). Not in that order, though.
It’s so fun, and is the most challenging level to me. (That’s right, Xen. You can’t hold three apaches to this pain bringer.)
Residue Processing
Hooray! After being nearly crushed by a Star Wars-esque garbage compacter, you only get rewarded for cheating death by getting thrown into Al Gore’s worst nightmare.
I love this one because it’s really just one huge obstacle course. Hopping from conveyor belt to conveyor belt, narrowly avoiding being squished, melted, crushed, splattered, blown up, irradiated, falling to your death, burning, drowning, and falling to your death. Also in the beginning, the three rooms of toxic waste that almost seem like a carnival ride.
“ALRIGHT, KIDDIES! DO YOU THINK YOU CAN HOP FROM ROCK TO ROCK TO GET TO THE OTHER SIDE OF THIS WASTE SPILL?”
“HEY KIDS! DO YOU THINK YOU CAN KEEP YOUR COOL ON THESE HOT WASTE SQUISHERS? GET YOUR TIMING RIGHT, OR YOU MAY BE SPLATTERED YOURSELF!”
“HEY KIDS WHO ARE NOW MUTATING INTO UNGODLY TYPE THINGS! TRY AND KEEP YOUR BALANCE, OR YOU JUST MIGHT GET ALL WE-MELTED! HYUK!”
Good times.
Questionable Ethics is a super neat chapter. I enjoy playing that section everytime.
Founded in 2004, Leakfree.org became one of the first online communities dedicated to Valve’s Source engine development. It is more famously known for the formation of Black Mesa: Source under the 'Leakfree Modification Team' handle in September 2004.