My memory of Half-Life… was when I first played it. That tram ride was SO memorable. And then the whole teleportation experiment in Anomalous Materials. I was pretty excited when I got the MP5 I have to admit… I never expected to see an MP5. Before you say I’m a COD fanboy… I’m not, so get that out of your head.
Games don’t need ironsights, that’s why you have crosshairs…
First time I was playing HL was, when i was 11…someone installed HL Uplink into the school pc, so i´ve played it …few months later, i´ve played the original HL …yeah, that loooooong, but exciting imbound ride 
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this^
I remember the Tram ride and the test chamber from when I was like 4 or 5 years old. Half life was the first video game I had everseen, and my god, was the game amazing to me. Video games were an amazing concept for my young mind. And the game looked very realistic.
Ten to Eleven years later, I got to relive those memories when I got the game on Steam. Played it over summer, and God, was there so much nostalgia .
Also, I was playing on Hard, when I got to some Blast doors.I ran up to them, trying to open them with E. An Alien Grunt did, and oh my god, did I scream like a girl. I shot it, and blasted it with some grenades, and just as I thought I was going to kill it, Another freaking Grunt spawned behind me. So, instead of trying to finish off the first alien grunt, I started taking out the other one.
God, did my hands shake after that. Half life has been the only game that has scared me like hell.
Has someone a memory for the explosive microwave ?
Scientist: GOR-DON! > 
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.