Yeah, a badass Klingon kid running around the Enterprise decking the adults would've been amusing, if crude and predictable. Turning him into a whiney, emo, sissy... ugh. Didn't we have enough of that with Wesley Crusher?
He didn't improve any on DS9. The only episode I liked him in was that Bloodlines episode, with his future self... who then attempts to murder his past self for the aforementioned reasons.