AC1 was visually stunning, and has kinda unique story, BUT the gameplay was meh at best, unbelievably boring... a racing game has more varieties than it.

Well, AC1 costume also isn't that normal in AC1 world...

At least different assassination methods ba... various scenarios like from windows, from roof, from water, disguise... or some additional requirements like total silence, 2 targets in a short time etc etc etc... Don't repeat the same stupid shit over and over again, barge in, kill the target, kill everyone else, mission completed.

Nope, you gotta replay the game
That's the only miss-able achievement.