Matter of opinion since judging from the tone of post not much of a Klaus fan. Don't care for him much either but do see that not many see it that way.
I personally like Klaus as a character... next to maybe Damon I think he does a better job of stealing any scene he's in better than any character on the show. Which I guess is why he's getting his own spin-off.
But I do think it's fair to say as a villain he at times comes off as anti-climatic. Really, for all the build up he got, he was essentially just a lonely guy wanting to make more hybrids like himself. As far as villainous agendas go, he was somewhat watered down... though again in hindsight that might be a good thing, if the plan now seems to be him carrying his own show.