Does enough visual and aesthetic things right that you can get a decent RPG vibe out of it, especially if you like the Renaissance. Combat is satisfying but unfortunately too easy. (Especially in the later games.) Free running does get a little monotonous, and this is the series that made "10,000 collectibles spread across the map" a signature Ubi tactic. But the game has quite a few titles behind it's belt and it's a pretty grand experience, all told, across the series. The story is.....it kinda boils down to derpy cliches, but it's reasonably well told. (Assassin's Creed 1 being my favorite.)
AC is pretty gamey in how it's structured, and the first one is the leanest (mechanically speaking) of them all. If you don't like what's in AC1 at all, chances are you won't like what's in later games. If you like AC1 but wish it had more, future games successively build up and round out more game mechanics, added to the core experience.
I like the series, personally, but even I got series fatigue during the 4th game. Once I get through that, AC3 will be like $5, I can play that in a year or so, and buy AC: Black Flag while they've probably put out two more games.
If you can get either the first game or the first couple for under $15, I'd say it's a decent gamble you won't feel like you wasted your money.