How essential is it to play Half Life 1 before playing Half Life 2?

If u don t play Half Life 1 u won t know the story trust me.
The creatures first apear in Half Life 1 that s when it all begins.
Play it!!!

Not too important. But you could just play Black Mesa. It's free and it's a done up version of Half Life 1

I've played Half Life 2 and really enjoyed it without playing any other Half Life, I would say you don't have to play HL1 :).

I'll never get the logic behind playing a sequel before the original...