No one should be allowed to be the head of the government or head of the state for more than 2 terms. 8-10 years are more than enough to bring about discernible change. Whether you acheive that or not, you must move aside and have others a chance.
My biggest concern about giving multiple or unlimited terms to a leader is complacency. They will only do the necessary for keeping their power. If they know that their core voters don't have an immediate alternative then they will also abandon their core ideology. So they go on doing the politics of appeasement.
Then complementary to complacency is their attachment to the throne, they feel like it belongs to them, the power belongs to them. They will do anything to be there. They can't imagine what they will do if not be the king.
I'm also fine with one term, but yes I can also understand one term might not be enough. But two terms are just right. More than 2 terms and they start feeling like they own the country.
But who's gonna listen to me.