The AK is a fine design, and it fills its intended purpose very well: a reliable, easy-to-fix rifle for peasant conscripts with little training. It does have drawbacks...it has vestigial sights, shoots a round that's ballistically inferior to both 5.56x45 and 7.62x51, has a stock length of pull that's only suitable for Siberian midgets in winter clothes, and can't be scoped worth a crap without buiding outriggers on the rifle. Even if you could scope it easily, it would be like putting a 200 MPH speedometer on a Pinto. The ergonomics are horrible, the safety lever is arguably the clumsiest solution ever put on a fighting rifle, and the trigger is mediocre and can't be tuned well thanks to the archaic cable spring.
On the plus side, the AK is sturdy as a truck, tolerates lots of dirt and abuse, and can be gunsmithed by a peasant blacksmith. Every design has its strong and weak points, including the ones designed by Moses Brownign and Saint Mikhail.