John Gill Commentary 2 Kings 18:5

"He trusted in Jehovah, the God of Israel; so that after him was none like him among all the kings of Judah, nor [among them] that were before him." — 2 Kings 18:5 (ASV)

He trusted in the Lord God of Israel
To be his protector and defender, and had no dependence on idols as an arm of flesh; the Targum is, he trusted in the Word of the Lord God; not in Nehushtan, but in him the brazen serpent was a type of, even in the Word and Son of God, his alone Saviour and Redeemer:

so that after him was none like him among all the kings of Judah :
for though Josiah was like him in some things, yet not in all:

nor any that were before him ;
from the times of the division of the kingdoms of Israel and Judah; and Ben Gersom and Abarbinel think that David and Solomon are not to be excepted; David sinning in the case of Uriah, and Solomon falling into idolatry, crimes that Hezekiah was not guilty of.