If you can find those combat skill books then you can make combat little more fun. Some books allows u to much easily parry and counter which leads funny enemy knock outs. You should try fighting pitt in Vatican, it really helps you get better at hand to hand combat.
I personally was relying mainly on stealth and disguises to freely roam around in areas. Every area has disguise that you can wear to freely explore without fighting anyone.
This game is puzzle focus exploration game with some action llinear action here and there.