When we first meet him he has just come crawling back to East Blue in an attempt to try and regain some of his former power by procuring the Baratie to be his new secret weapon pirate ship, so that he can use it for sneak attacks. These dirty tricks of his show his lack of true fighting spirit. This is realized by Luffy especially when he disregards the safety of his own crew to win a battle. No matter how many men or weapons or tricks Krieg employed he was defeated by one man Luffy.
As Krieg went i did not care for his character on iota. He was rotten even by pirate standards and the gran scheme of things was a very small pirate. the character design as fine and had its unique traits. However, the character itself was limited and was just carbon copy of lots of greedy uncaring villains that have come before him. Feel free to let me know what you thought about Krieg in comments and such. While he was a challenge to Luffy at the time I would not even come close to labeling him a great villain or even worth remembering as compared to others created by Oda.