I think people shit on the first game way too much, which is odd to me. The game was repetitive, but hardly bad. I loved it when it first came out. I think it's because AC2 was such a leap forward it made AC1 look bad.
People forget how ground-breaking AC1 actually was, with the large crowds, freerunning, open world, and the verticality. It's all familiar (and maybe stale) to us now, but at the time it was nearly unprecedented. It took some time before Ubi managed to make a great game out of it, though. All those new game mechanics, and they didn't quite know what to do with it. AC1 is a fine game, and IMO it doesn't really deserve the hate it sometimes gets.
I think it was actually fine as a game. I think they knew exactly what to do with it but they just didn't realize the full potential. I know the story was the best for me. I never liked Ezio and it really started going off the rails in a bad way in AC2. I don't mind a little bit of cleverly done sci fi but aliens and all that stuff - that was just too silly for me.