Well, if you're speaking from a story standpoint, you could probably skip the first one and go right to the second if you wanted... the story to begin with is fairly basic, and there are only a handful of callbacks to the original game.
Gameplay wise, again, you might be able to skip the first... the second plays just like it, only it adds a whole bunch of new elements on top of what the original started.
Of course, I can't tell you how either relate to the third game... so if there's something in that one linking it to the previous two, you might miss something.
I'd say it's worth playing both... but then again, I really liked both... I can't say what you will think of them.