I think the standard running speed is too fast. It should be toned down a fair bit to match approximately Skyrim's.
The world would feel larger and more realistic plus it would enhance a more tactical approach to combat if you don't just run through everybody.
I take my experience from Mount&Blade where there is a very low running speed. You build up your speed the longer you keep running without a break which still won't be closely as fast as ESO's. Since you cannot get away that easily you always want to have some comrades near you to be a force to be taken seriously.
I would have toned down the standard running speed in ESO by 20%. Having a mount will still increase your speed.