Not so important in terms of the ancestors' stories which takes up most of the games. But you'll want to look into the Desmond cutscenes on youtube or read it up on wiki to understand what he's trying to do.
I personally didn't want to buy the other few games either, so I just watched the story cutscenes on youtube
I never managed to finish the titles I played previously in the series(1 and 2, just got bored of them) and never touched brotherhood/revelations but i picked up this title and I've fully enjoyed it. So you should be fine.
The backstory I learned from watching my friend play the previous entries and tell me what I missed.