I have been told that Krav Maga is too simple to be effective.Is this true?

You're right to find it hard to believe! Krav Maga is way more effective than anything else you'll find Stateside. All the stupid katas and fancy movements you learn in traditional, "pretty," martial arts will never work. However simple the movements and ideas in Krav are, Krav itself is not a simple entity. Imi Litchenfeild painstakingly scrutinized all of the martial arts and took the most effective tactics from all other combat arts. Krav is like a designer drug of martial arts. AKA the best thing ever.