If a surprise forces me to change my plans, I will not like it one bit. If they do not, however, I will rarely have a positive reaction (unless it is evidently linked to my interests), but neither will I dislike it.
I do tend to be uncomfortable with wrapped gifts, though, when you are supposed to look positively surprised and pleased. Since it does not come natural for me, my mind has to work a lot to know the proper emotion and reaction for each thing that is revealed to me, which makes it a stressful experience.