It is the best thing you will ever do for yourself! I quit about 15 years ago after smoking 35 years. I can't stand the smell of cigarettes now. If a smoker walks by me, I can tell in a heartbeat.
My sister is a nurse and she checked my oxygen level and was impressed that it was so high since I am a former smoker. She said it just goes to show that you can recover your health after you stop smoking.