The Bible talks about the 'greatness' of Nebuchadnezzar's kingdom and his ability to conquer nations at wil. Do you think that Nebuchadnezzar was in the end a 'good' person or bad? You will need to have prior knowledge of the story of Nebuchadnezzar and his interactions with the Prophets in order to make a judgement.
When it comes to Nebuchadnezzar, we have basically only one source to draw on, the Bible. Nebuchadnezzar is recorded in Daniel, 2 kings, 2 chronicles and Jeremiah. After Daniels prophecy (from his dream) that he would live like a wild animal came true, he supposedly roamed around for seven years eating and living like an animal. When he came to believe in Gods ultimate authority his sanity returned. With that, his honor and his kingdom also returned. He started praising God and his kingdom was more glorious than ever before!
The question you have to ask is did he praise God because he didn't want to be crazy again, or because he truly believed in God. Remember, this man had other dreams that Daniel had told him about already. He had seen God write on the wall. Yet he still did such things as build huge gold statues to worship, and throw three hebrews into a furnace to burn. After watching God save them, he still didn't repent. It is not unrealistic to think that he wasn't so much a good person, but afraid of what God would do next. Fear is a powerful motivator, and he had seen what God could do.