I've heard a lot of guys complain about archers and shields recently and this is what I have to say
I'm a shielder and I'd say that our biggest enemy isn't archers and crossbowmen but lame ass AGI-whoring über-buckler- lamers
Everything we can do they can do better. Block arrows check, block everything else, check. It makes no sense at all. Bucklers were used commonly, yea, but that's because they were easy to carry around not because they were more efficient than real fucking shields.
Vikingr, the only mod with somewhat realistic and fair combat, has the shields all right. If your shield is too smal to cover your entire body, you risk getting hit by missiles. If you cover your head you might get hit in your legs and vice versa. MAKES PERFECT SENSE! I'm a shielder (I prefer to use cheaper, better looking shields that actually go with my outfit rather than whatever has the best stats (like a buckler)) and I say make it so. Not only does it take quite some skill to be able to block every single incoming blow with a small buckler, especially when you're attacked by multiple opponents, but it takes ninja-like skills to block incoming missiles with a shield the size of a dinner plate. If the shields actually worked like they do in Vikingr and in real life big shields would actually be usefull. Why d'you think crossbowmen carried pavises and not bucklers? Size matters.
Also. Make the shields work as described before, they only cover what they actually cover, and make the big shields require less shield skill while adding a STR-difficulty. Using a huscarl shield or a board shield for blocking attacks would be far easier than blocking with a buckler, though it would take more strenght to carry them around and use them properly.
Nerf bucklers. Just not fair that they get to block arrows coming at their toes while only covering their left hand and part of their torso.