There's one thing you should add to Holmgang, and that's that it's also a Draw-In skill/bind skill. So if you use it, make sure it's not before some mechanic that'll require you to move. There's nothing more unpleasant than being held smack-dab in a telegraph due to holmgang, and it wearing off 0.5 seconds before the attack hits, resulting in death.

And while it's probably a waste of a cooldown to do so, it's a lot of fun to sneak up on an enemy that isn't bind immune and holmgang them. A good six seconds of them standing there being unable to turn around and attack you.