I would rank them, having finished all 4
AC2 > AC Bro > AC Rev > AC1
AC2 is just an all-around great package and a straight up sequel to AC1 which was like paint drying, not to mention the introduction of the WTF?
?? endings that soon followed (AC1 was hardly a WTF ending). Tons of stuff to do, collect, and lots of mysteries dangling at your face like a nice half chub cock.
Bro is just an extension of 2, with some additions, like the Hidden Tombs, which were nice fun diversions. The growing of your own brotherhood and firing arrows and such were awesome and it was fun to send them on missions and level up. Ending was a good WTF but lacked the kick of AC2's. Multiplayer was also well done and thought out, surprisingly, and not just an add-on.
Rev is once again an extension of Bro with some small additions. Why did I rank it lower than Bro? Series fatigue, mostly. It doesnt really do anything to make it stand apart from Brohood. They removed the tombs (except like 2), had a collectathon that was over at not even half way (the rest unlock... nothing!). The Desmond Stories were flat, they really could have built on this but nope. The introduction of Sixteen was also a complete flop, especially after his enigmatic speech at the end of Brotherhood, instead he's this dopey guy who wants to leave badly. The story goes nowhere, not even interesting. However, the final send off for both Altair and Ezio were done amazingly. Made the whole journey worth it. You wont miss anything by just YouTube-ing it though.
The Tower Defense is only done once in a tutorial and you never have to do it again, since it only occurs if you fuck up a lot with the Templars. They built on the Brotherhood aspect by introducing more things to do, and even cities to take over. Multiplayer is more or less the same here, with a few tweaks.
AC1 is just wack. All the other games do a much better job at handling Altair. If he wasnt such an integral part of the mythos, Ezio would pretty much be Assassin's Creed and it would be all the better.
