For anyone who knows about shields, historically and otherwise, they know that shields are one of the main things that are simply treated incorrectly in almost anything they are used in, from games to movies, etc.
When it comes to history there is a reason that the buckler, which was one of the smallest shield types, was used longer then any other shield in many many different battle situations. It was simply one of the best and most versatile shield types throughout history.
Shields all had their weaknesses and were better used vs certain situations. The bigger shields would be better suited for defending vs archery or formation based defense, but they were bigger and heavier, not as quick/agile as a buckler.
The advantages of using a buckler in terms of melee fighting:
1. Quick and agile, able to quickly block strikes
2. Held in hand instead of strapped to arm. Thus people couldn't grab your shield and pull you down/throw you off balance.
3. The shield could be used offensively as well. Bucklers could be made to have sharp edges, this could be used to cut someone. Also handy for an off hand punch to throw someone off balance.
4. Defense modifications. There was the famous "sword breaker," basically a spike that was put in the middle of the buckler which over time could harm/damage the enemies eapons. There was also the sword catcher, basically a "latch" type of thing that could catch someones sword (if you blocked it right) and then you could pull it/disarm them.
The main disadvantage to the buckler was against missile attacks. The area it blocked was small and suited toward blocking melee attacks, not ranged.
I would like to someday at least see a game that treats sheilds more realistically. Gives ALL types advantages/disadvantages and doesn't simply make them bigger = better and treat buckelrs as the "crappy starting shield."