"People didn't like when this was misnamed as "Letho Sex Scene".
A quick walkthrough since I've had more than one friend complain about Letho.
Mostly used Yrden even if you can get streaks of bad luck and have it not work for several consecutive times. It is, as far as i know, the only way you can get to hit Letho's back so you can easily pull three or four strong slashes on him.
I don't like knives or bombs against Letho, mostly because he's really fast at casting or throwing his own bombs and is likely to end up ♥♥♥♥ing you up as you're throwing (which takes ages anyway). His spells are obnoxious. His Aard is ridiculously fast and luckily lacks range, which is compensated by his slower Igni that not only pretty much reaches the entire room but burns away more than half of my health with a Kayden armor on.
Don't like the fire spell because it will hardly stun him; don't like Quen nor Quen spamming in general because it hardly changes anything against strong enemies but i admit it's a good time waster (i guess it's good if you are on Swallow or something). Remember Quen can't save you if you'll act like an ♥♥♥♥♥♥♥ and just roll your way into a bunch of enemies."