Shampoos and how we react to them is very much a personal thing based on individual sensitivities, some people like Head and Shoulders shampoo for example whereas I think it's rubbish, made my hair look like straw the one time I was forced to use it on a school trip.
Try using a moisturising conditioner after using Nizoral, I noticed this completely ameliorated the drying effect that ketoconazole shampoos can have on your hair and keep in mind I'm using the 2% formulation which is said to be more drying. I use Tresemmé Naturals Nourishing Moisture Conditioner. My hair and scalp looks and feels no different on the Nizoral days than on the off days, if anything it feels rejuvenated and fresh right after shampooing with Nizoral!
Oh and while this may be a no brainer, don't leave the Nizoral on your scalp for the duration of the shower like some people tell you to do, that's not how it was designed to be used and that is not what the instructions on the package insert say in terms of proper usage, use it like this:
Apply a palm sized amount of Nizoral to your scalp and massage it in. Leave it in for 5 minutes and then rinse it out
Apply a moisturising conditioner and be sure to leave that in for 2-3 minutes. Rinse that out.
Hope that helps!