Dual wield is all about power attacks. You cant defend, but the damage is huge.Once you get the relevant perks you can rip apart just about anything in skyrim.
Also, not exactly related to dual wield, but I found a fun little sneak attack move. With the silent roll perk and charging power attack, if you hit sprint while sneaking and do a power attack, you will do double critical and a power sneak attack if you are successful. Just have to make sure you do it from behind...

Meh, can't type properly from the phone.