Halo 1 was simply the first FPS I played on a console that wasn't a steaming pile of crap/was actually a great game in its own right.
I have played Goldeneye, PS1 shooters, PS2 shooters but Halo was the first one that was actually any good/compared favourably to the average good PC shooter.
Health regen:
So I don't have to run all over the map/run halfway back down the level to pick up a health pack. Hunting for a health pack because I took a stray grenade blast is the definition of annoying and you never know if theres a health pack in the next room or a whole bunch of guys waiting to blast you back to the last checkpoint.
AI
Halo has won awards for it. Need I say more? Btw before you think that because the AI didn't pwn you hard doesn't mean it couldn't have. The AI would never miss unless by design.
Story
The story was pretty gripping from the get go. It was possibly the best opening scene I have ever played in a FPS game.
etc.
Tease.








