Well if he's coming across as unintentionally funny (like Bane in TDKR) that would be even worse. I thought he was genuinely funny, like the frisbee line was actually meant to be funny and that was my favorite funny line in the film. He was intentionally funny!

And I loved him that way. I wouldn't mind a more serious Ultron in the future though.
I didn't mind him being funny or snarky at all. He should have been more of a physical threat. Seriously, the Avengers were OP in this film. I get the theme was "Gods and monsters" but I felt Ultron never stood a chance (and he knew it), so he was creating Vision. But even then they stole Vision. I was rooting for him more than the Avengers in this film.
I thought Ultron was fairly tense for a while at the start, but after the Vision gambit was foiled, the tension just collapsed, for me. Ultron's plan up until that point had revolved around upgrading himself to the point of invincibility.
When the heroes stopped the Vision upgrade... did Ultron have anywhere left to go? Vision is super-Ultron, so once the Avengers nicked Vision, where was the threat? The Avengers already have Ultron-but-better on their side, and moreover, for the entire film up to this point have demonstrated a consistent ability to defeat Ultron drones. Iron Man killed one in Wakanda, Cap went toe-to-toe with one for a surprisingly long time, and the film seemed to go to an effort to avoid the Hulk or Thor ever taking on an Ultron drone dirrectly, if only because those two are the most powerful Avengers and would crush him.
So the tension was that, while Ultron was an inferior combatant to any of the Avengers' heavy-hitters (i.e. Thor, Hulk, Stark, roughly in that order), Ultron's near-limitless ability to respawn helped to create a tense cat-and-mouse chase while Ultron went about building an upgrade for himself, which would finally get him to the point where he can take on the Avengers directly.
I was afraid he might get defeated before we get to see his master plan. Though His arrogance is what defeated him. Seriously, he waits for the Avengers at the end and send a his whole drone army after Thor taunted him. I loved his talk with Vision at the end though.