I've been saying forever that Martok is the best Klingon ever. Every moment he is on screen is pure gold. I like his addition to DS9 even more than I ddi Worf's. And I love his professional relationship with Sisko. They were such equals and the two actors had a wonderful onscreen chemistry. I would've loved seeing more Sisko-Martok scenes.
Oh, and the character was pretty cool in his previous life as well as a doomed Vulcan captain.