Do I need to begin from the first game for the story of Assassin's Creed?

I've got the original Assassin's Creed game somewhere in my house. When I finish a game I then intend to play it, but it seems to "move" and so I begin another game instead. Been going on for two years+.

My question is, should I bother with the first Assassin's Creed game? I know there are a lot more out there now. Will I miss a lot of the story if I were to jump straight to the second game? Or Unity?

Should I begin from the first game or are the later ones so much better that missing some of the story does not matter?

Coming from an Assassin's Creed Veteran I'll say you have some choices.

1st Choice (Not caring for the Story):

If you really don't care about much of the story (which I assume isn't the case because you made this question) you can easily jump into any game.

Maybe if you jump into Brotherhood or Revelations without any previous knowledge you'll feel quite lost.

2nd Choice:

If you care about the Story and don't really feel like playing the first game you can opt for Assassin's Creed 3 which gives a brief but good sum of the story of the Modern Times of the Series.

But to answer you answer completely, I feel like the later games are much much better and the story in Assassin's Creed 1 isn't substantial BUT it comes down to what you want to do.

Like the 3rd Crusade era? I would advise you to play it.
Like a good story with some philosophical thoughts? I would advise you to play it.
Don't have much time to play and you have to choose between 1 or a later game? Well I would advise you to play the later game and read a synopsis online or see a walkthrough online.

If you want me to explain further and want more convincing please say so in the comments.

This is matter of player opinion. There is a story in Assassins Creed which involves a person in experiment where scientist inspect human dna and get's back into the history seeings the events by itself. If you just want to enjoy the gameplay mechanics and the story which happens in actual gameplay, you can just start any series. But if you want to know the other story which happens behind the "curtains" you need to start from part 1.