Yea, Half-life 1 is quite cheap and worth it as there are plenty of modifications that are just awesome, such as Sven-coop and Earth's Special Forces.
[SIZE="3"][COLOR="DarkOrange"]I second with Skyrider on this one, but I like the game a bit more then the mods. It’s got a great story line, good A.I., cool weapons, and the price is right (really cheap for such a good game). I would say [COLOR="#ff0000"]HL:S[/COLOR] is the way to go (It has better graphics and better physics and a few changes here and there) but if you are wanting the good old [COLOR="#0000ff"]HL[/COLOR] experience (worse graphics and glichy physics) then I would say go with just normal [COLOR="Blue"]HL[/COLOR]. They are both available for purchase on steam for $9.99 (currently). Then there is [COLOR="#00ff00"]HL2[/COLOR], but I would play [COLOR="Blue"]HL[/COLOR]/[COLOR="Red"]HL:S[/COLOR] before thinking of playing [COLOR="#00ff00"]HL2[/COLOR]. There are also (as Skyrider said) many great mods out there for both games. [COLOR="Orange"] Hope this helped.[/COLOR][/COLOR] :)[/SIZE]
[SIZE="1"][COLOR="#ff0000"]*HL:S: Half-Life: Source[/COLOR] [COLOR="#0000ff"]*HL: Half-Life[/COLOR] [COLOR="Lime"]*HL2: Half-Life 2[/COLOR][/SIZE]