Soldier
in Assassins creed II there will be 5 enemies, as opposed to the original Assassins creed where you fight the same guard type over and over, with the exception of archers.
one of the new guards is the "agile", which, as the name suggests is a very fast, lightly armored enemy. they also have the ability to climb and run around rooftops like Ezio, leading to chase sequences.
next, theres the archer, which is a guard, armed with a bow and a sword (for close combat)
there is also the brute, who is just that, a heavily armored, heavily weaponed (weapons such as maces and axes), and rather stupid guard type. their armor will cause a problem for some people, but it also makes them slow and cumbersome. they will also not be very intelligent, and therefore will not be able to pick you out from anyone else in a crowd.
there is the standard guard, who is just that. they are armed with a sword, and aren't particularily fast, strong, or smart
and finally there is the seeker, who is often called "paranoid". they are a special guard type, because they have the ability to check haystacks and the like, when Ezio does a leap of faith, although ezio can counter kill the seeker if that happens. they are armed with long spears or halberds (a very long spear with an axehead at the end) which let them check haystacks, etc.