The Tiger II had a few problems.
It used the same engine as a Panther, and a similar transmission as the Tiger I but with 15+ tons of additional armor. That was murder on the transmissions to move these hulks around and that was a (or the maybe the worst) major breakdown problem.
Another problem with the excessive weight was getting it across some of the smallish bridges in Europe. 70 tons was too much for all but the main bridges so this in turn limited mobility.
Due to a lack of strategic materials, the Tiger II armor was sometimes inferior in quality to it's original design. However, the armor was thick enough that it was still very effective.
All in all, I think the Tiger I was a more effective tank than the Tiger II. It had a better balance of firepower, armor and mobility while being more reliable.
