AC1 was rather painful for me. I could barely do two assassinations as one of them just had me chasing the target for ten minutes straight with no real way to catch up. Guards would hack me into giblets from the slightest provocation.
Thankfully, AC2 was much better. I was able to catch up in the storyline moderately well and I even beat it. I haven't done Brotherhood yet, sadly.
Still need to buy AC2 again so I can do more sandboxing.
that's probably because AC2 fixed most of the repetitive missions from the first game, and the free-running and climbing was faster so it wasn't as boring.