I'm fairly neutral on Markarth itself, as was said they city is full of annoying and downright distasteful (heh) people but I love the dwarven ruins/city set pieces and the vertical design with all the waterfalls is quite lovely to look at so it kind of balances out between those factors I suppose. The force-greet quest NPC along the main path to/from the keep doesn't help matters much, I have to say.
What I dislike is how the city is placed geographically in the game world, like it's in a pocket corner of the map. There's only 1 way in/out (I use fast travel rarely) and the lack of any surrounding explorable territory around it makes the city feel extremely isolated and cut off from the gameworld. If you want to get to the city, you always have to take the main route up to the main gate past the farm and then the carriage and then the stables, where as for all other cities/towns there are alternate paths or entrances or both - sometimes quite a lot of each. It makes using Markarth as a main base where I have my home (I've only purchased Vindral Hall once in all my time with this game) and primary storage very annoying to the point that I never spend more time there than I have to, which is kind of a shame as visually the city is quite striking.