For people playing Half-life 1 for the first time now, there's no way you can really appreciate all that it did new and revolutionary for the FPS genre
Before Half-life came out this was the state of FPS games:
- There was a serious push from devs & consumers alike to the thought that FPS single player games were on the way out. That multiplayer was the only thing worthwhile for the genre.
- Single Player campaigns were still stuck in Doom-esque level designs. You had a random ass set of levels through together with the only real puzzles being "Find the Red Key"
- No attempt of any narrative in FPS. You mission = kick ass!!11! and kill things
- Enemy AI was still essentially enemy see's you then chases you until it dies
- Ammo & weapons just randomly floated in areas
- No Friendly AI characters existed. It was only you and enemies
What Half-life brought to the FPS genre when it came out was the following:
- Through the use of scripted events it immersed gamers in ways never done before. Just the intro alone set the tone for the rest of the game. You saw the complex through the track, got a feel for the place, interacted with the scientests & guards, and actually was there when the shit fell apart. On top of that the scripted events later on pieced together what was going on (crab killing scientist, black ops killing scientists, monsters wiping out guys, etc)
- It had amazing level design that not only made sense to a "real world" (no hidden strange doors, or passthrough walls,etc) but it all connected. It wasn't like quake, where at one point you're in a castle and the next level in some hell zone. It worked your way through the whole complex but it was seamless. It wasn't Area 2-3, etc.
- Black Op AI was something never seen before. Enemy ai that would work together, and if you tried the Doom "hide behind the corner and wait for them to mindlessly run into my bullets" tactic you got a grenade dropped in your lap instead.
- Boss fights that actually had more puzzle and strategy than "shoot the big gun at it"
- Amazing sound design for the times
- Co-op characters that would help you out throughout the game. Granted they didn't last long but it was a first.
- Enemy vs Enemy battle scenes. Finally there were times where you'd just wait for the aliens & soldiers duke it out first before entering the fray
- Weapons, ammo & health packs that were placed in areas that weren't as random and crazy. Sure it wasn't completely realistic. But you got health from the wall stations, or from crates. Same with weapons & ammo. It wasn't just rotating and floating in the corner of a hallway.
- Not action all the time. It wouldn't just have pure action all the time, it knew how to crank it up and then slow things down for a while. And the puzzles in the game actually made sense. And they'd use signs and visual queues to aid the gamer as to what to do w/o any tool tips or some abstract voice jumping in to tell you what to do next.
The problem is all these things are taken for granted now. For example Halo really started with the Half-life template and then put their own spin on it. Evolved it some, and did their own thing (although level design would never be topped).