Damn. I know this game's old, but not that old, and some people say it does not hold up - dude, it pretty much does.
Assassin's Creed is a stealth-based videogame, with action and parkour aspects that enhance the experience. The gameplay in this game feels somewhat old, but it's ok nonetheless. And the movement - that shit is really something.
The locations as well as the atmosphere are pretty good, too.
And for the story, it is actually very intriguing how things will turn - for the bad or for the right, for your enemies or for your creed. It presents a dilemma that you'll have to face, whether you like it or not.
For what started the saga that we know nowadays, although very repetitive, the first entry is a very good videogame.
And for those who say it's bad, that's because you never played it.
Give it a try!