The greatest FPS ever created.
It set the standard for FPS games of the future and any single player FPS games after HL are always compared to it. Still though nothing has really done for the genre what this game did, and i don't think anything will until we really advance on tech to step it up a notch.
With future games like Bioshock and Crysis coming i'm sure they'll do great but still i don't see anything coming out that will make us forget HL. I can't wait to see something that does :) Not even HL2 could produce a game worthy enough.
Now for todays standards the gameplay is pretty basic but it still holds up and i can't wait for a fan made remake called "black mesa source". However it's still very fun but it wont make a impact on you like it did in them days.
Back then though it was amzing how it was all one level and the graphics look awesome and the AI seemed like the greatest thing ever, i just remembered how it took me like a month to complete first time it was soooo long!
The sounds and graphics were also amazing but now they seem pretty dated and quite right they are lol, nearly 10 years.
I suggest everyone to play this game at some point in their life to just be able to say they played the original HL game :)