That was my biggest problem in AC3, and why I quit the series.Not much IMO. I found an area where there were endless guards and I got into a rhymthm and killed guys without getting hurt for like 15 minutes. There really is no challenge, but damn do you look cool pulling off moves.
I made it through the entire game using only a hidden blade and a starting tomahawk (except when mission demanded a specific weapon).
There was no need to upgrade, loot, hunt or anything else... It was simply boring and repetitive.