I like Capitol because it is less overwhelming than some of the other shopping malls in Istanbul,…read moreand it has a fairly nice selection. It's one of the more....er...uppity? malls in the Uskudar/Kadikoy area, but it has an HD Iskender and a Flo, so that is a major plus. Amazing fountain. One drawback is that there's no large electronics store (just a baby Teknosa). But they do have a Biletix, which is mad convenient.
If I'm being forced to shop, I would definitely choose Capitol. At least I don't have to fight off over-attentive sales associates and there's no one assuming I'm a tourist. I think those are its best assets.
It's also wonderfully decorative during any season. When you walk in, you feel reeeeeallllly luxurious (for Uskudar).
If you're in the area, not a bad bet. Parking is a bit expensive, so avoid it if possible.