Glad I ticked off UAE via work, it's a place that doesn't remotely interest me for personal travel.
Burj Khalifa is alright, for some reason I did pay for the 'premium' option, as there were no normal tickets left (did it on a whim). It is impressive yes, but wouldn't bother again.
My biggest gripe about those cities is that everything is so far from everything else, and it's not a city where you can just explore by foot and discover things along the way.
The old market bit is quite nice too if you've not experienced any middle eastern culture I guess.
The Sheikh Zayed Mosque in Abu Dhabi is very impressive if you ever make your way across that way.