I have 2 in my library. It's been sitting there for years, the one Steam purchase I regret. If it really is the best one, maybe I'll install it.
By all means, do play it. But keep this in mind: as soon as you start feeling bored with the game, stop playing. Don't do as I did and try to finish it, or you'll end up hating it (yes, not just disliking, but actively hating the monotony, tedium and repetitiveness of the game, and how horribly stretched it is, and wishing with all your might that the game would soon be over). You can go back to it in a year or two, but don't force yourself to keep playing.
If you do that, then you may like it. It's not bad, it's just... I don't know, picture your favorite Pink Floyd album (if it's anything other than The Division Bell, you're a bad person and I don't like you) but with only one song. A good one even, like "Wearing the inside out". OK, now imagine that you make it a triple... no, quad album with that same song over and over. Now, when you think you're about to finish the album, you find out there were 2 more CDs you missed at first, which are also made of that single song, so you gotta listen to them too if you want to hear the whole album. There's another disc of bonus songs, but they are demos or different versions of the same track, so they are optional (fortunately), with the exception of a really long and boring one that's placed at the very end of disc 5.
I think that's a pretty accurate description of Assassin's Creed 2. The material Ubi had to work with was good; stretching it to the point of ridiculousness was not, just like the album I imagined would be.