I love Gallowglasses. In my online games in Viking era I usually play as the Irish, with a bunch of Bonnachts, Kerns, some cavalry and gallowglasses.

The Kerns receive a charge, the Bonnachts which are directly behind use their javelins and run in to pin the opponent. My cavalry and Gallowglasses take on any opposing cavalry if they are on the flanks before running in to hit the opponent's infantry from behind.

I always find it comical to see heavily armoured Vikings running from what are effectively angry farmers armed with pitchforks and pointy sticks.