I'm thinking about picking up one of the Assassin's Creeds (1,2,3, brotherhood, revelations) before the sale ends. Which one should I get?
AC2 is probably my favourite.
Brotherhood was also very good, but I felt limited being stuck to Rome (although Rome was done really well).
Revelations was similarly good, but against felt limited in Istanbul.
AC2 is probably best to get out of those 3 though, since brotherhood and revelations are sequels.
AC1 is a great intro to the game, but I think it can be considered fairly repetetive (moreso than the others I find).
And it's not necessary to play AC1 to play the others.
AC3 is a good game and it's nice to go back to multiple cities with expanse to explore too.
Game felt slightly short for me, but it's worth playing if you're into the series. It's also the ending of the Desmond Miles storyline, so if you enjoy that part when you play AC1/2, then definitely play AC3.
Black Flag is brilliant and if you get a chance to play it then I suggest you do, but I won't go on since you didn't specify it.