If the surprise villain was actually done well and wasn't obvious then I don't mind surprise villains. Prospecto and Turbo were actually a surprise to me because I didn't see them coming and they were done well as actual surprise villains. Hans was a poor surprise villain and there's some villains I see from a mile away like Screenslaver (I knew who the villain was the moment the character was introduced)

Depends. Sometimes they're good, other times they're lame

For me it absolutely depends. I like watching villains turn into villains (ie they weren’t at the beginning of the story but they are by the end) like Morgana, but that’s not quite a surprise villain. Thinking of my favorite villains, most of them are preestablished, although my absolute favorite villain, Ben Linus, was kind of a surprise. It didn’t come out of nowhere, but his first storyline was all about “is he a good guy or is he lying through his teeth”, so we didnt know for sure until the end of the season. Which was a cool middle ground between these options, I think.

Depends of the story and genre of the movie I guess. Somehow they work well (like, Bellwether from Zootopia) but some others are felt way too rushed and forced to be a hidden villain (like, Hans from Frozen)

Nope, because Disney's "surprise" villians not surprise at all....they were predictable.

I like the surprise factors, but the villains themselves were very weak and in Hans' case, nonsense

I don't think all Disney villains should look sinister and have a sinister laugh. Not all dangerous people are like this in real life. Some villains that don't look or laugh sinister can be no less and even more ruthless and dangerous than ones who do. I find the opinion that villains should be like Shan Yu with inhuman eyes, grey skin,claws and sinister grin shallow. I find it so shallow to say that only villain with scary and sinister appearance and sinister laugh are scary and badass and the secret villains are "too kid-friendly and lame".
I've read about one real-life greedy Bluebeard who was just like Hans, pleasant -looking.
But really depends on writting.

Generally this, but some surprise villains (Turbo, Te Ka) work well.

I really depends on how well it’s done. My two favorite surprise villains are definitely Bellwether and Lotso, and I think they have a lot more depth than your standard cartoon villain. Then you’ve got ones like Hans that come out of no where.

In my country surprises are for babies who still watch the Rugrats.

Either, so long as they are well-written characters.

It's fun to have a villain who we know is a villain, Disney hasn't done this in a long time. As for surprise villains, it's okay as long as it's not predictable. The only movie I thought did this really well was Wreck-it Ralph because it seemed organic. For Zootopia, Frozen, and Big Hero 6, it felt more like "Let's pick who the surprise villain is gonna be first, and then we will write it into the story".