I don't know why people act like the first Assassin's Creed is somehow obsolete. It has:
1) A completely different story.
2) A completely different setting.
3) Altaïr the badass (vs Ezio is the ponce).
4) Better story if you pay attention to it. AC2's story was a contrived cliché-fest focused too much on that muppet Ezio. AC1's story was driven by more subtle sub plots.
5) The best combat of the first 4 games. After the first game, the combat got too smooth and flashy. Although they carried over most of the mocap from the first game, the new moves they added were too fanciful. As I've said many times, despite having less variety, AC1 combat was raw and visceral and puts the rest of the games to shame.
6) Half decent mouse input. I've only tried the first four games, but aside from AC1, they all have appalling mouse acceleration. AC1 still has pixel skipping, but at least it's playable.