For me the Museum of Anatolian Civilisations alone merits a visit to Ankara. In my opinion the most fascinating and beautiful archaeological Museum on the Planet. The area around the Ankara Kalesi is nice and definitely worth exploring. Ankara has beautiful parks and fine dining. And then of course there is the Atatürk Mausoleum.
Taksim area particularly in summer is dreadful. But then there is so much more to Istanbul.