The original Half-Life that you remember is very different to a 1997 alpha preview build that was offered to the press, but now you have a chance to try out that build for yourself.
A 1997 alpha build has been shared online by Reddit user Jackaljayzer. You can find a download link here. Some people believe that this build has been leaked on purpose to tease an upcoming Half-Life 3 announcement. If true it would be a pretty nifty piece of marketing.