I find it strange that I don't have these problems. The 360 version can't be that different to the PS3 version, can it?
Yeah, sometimes I jump to death when I actually want to jump to the next building, but not very often. Hunting down Borgia messengers and thiefs on the rooftops is great fun. And the combat system is awesome, in my opinion. You always fight the guy who is targeted, and you can switch the targets with the left stick. Disarming and counter attacking is easy, too. The more you train in Monteriggioni, the easier it gets for the character to tackle more difficult enemies, too.
The only problem I had was the sideways jumping technique you learn in the last Assassin tomb. That took a while until it worked properly.
The thing I'm finding annoying about the assassins tombs is how they've gone for an almost-but-not-quite-Tomb-Raider camera, which sometimes makes it hard to line up where you're going. And which makes me default to using Tomb Raider moves, which don' quite work cos this is a different game...
That and the fact that you can't go back in later to search for the secret areas you missed.
Don't get me wrong - I do love the combat system and it's great 90% of the time. I just don't think it's quite perfect, and I wonder if it's stretching the capabilities of the 360.