My rating is for s1 to s4. s1 to s4 are brilliant. They have good storyline, good amount of suspense, humour, and emotions. After s4, you may or may not watch it, it's upto you. It'll get boring, especially if you're not that attached to Iris. S6 is still better than S5. But neither s5 or s6 will be able to give you those s1-s4 vibes.