My H has been taking it for about 5 years now. He's found it positive overall. At a really high dose he felt irritable, so he dropped it back down and it works well for him. The only side effects were appetite suppression at first (that wore off though) and sleepiness when it wears off in the evening.
Concerta was a miracle worker for me but after about 5 years it just stopped working. I have yet to find anything that works as good for me. Like all meds, ADHD meds are funny in that they work very differently for different people.