I would say that "spoil" is the most negative. FDMaxey had a good explanation of this word. "Indulge" is more neutral. It will usually be sort of like "giving in" to a person's desires. Like if my child asks for ice cream for dinner, I will not think that is a good idea. But on his birthday I might make an exception and "indulge" him. ("Indulge" can also be used as a euphemism for giving into to oneself, as over-eating or something like that. The idea is that a person doesn't have any willpower to overcome their desire for something they shouldn't have. But it is usually used to try to be polite about their lack of discipline.) To "pamper" someone is usually positive. It is used typically when people work hard and then get to enjoy being waited on. A common use is to talk about moms taking a day to get a facial or massage. It can also be negative if the person you're talking about expects to be treated that way all the time. I think that pamper is usually a more positive word than indulge because most people (in America, at least) agree that hard workers deserve some respite from that now and again. Also, I agree with fdmaxey's explanation of "over the top" and "excessive."

"Indulge" means to allow yourself or someone else to experience something enjoyable. It can also mean to use something harmful like alcohol or cigarettes, but it still has a more possitive sense then "spoil" or 'pamper'' 'Pamper' means to treat somebody in a very special way, with a lot of attention. A spa where they give you a massage and sauna would usually talk about pampering. It is not regarded as positively as 'indulge', but it is still better than 'spoil' 'Spoil' is the most negative of the three. It generally gives the picture of someone given undeserved special treatment to the point that the person (often a child) comes to expect such treatment. It can be used in a joking way when someone says to someone else "you're spoiling me' , which means 'you're giving me very special treatment, which I appreciate." The three terms do overlap. You could replace 'spoil' with 'indulge'. However, the terms are not exactly the same. "Over-the-top" means extremely excessive. It is a stronger term than just "excessive".

spoil someone means treating someone with an excessive generosity, giving everything someone wants. (materially) pamper someone means treating someone with great comfort, taking great care of someone and doing everything to make one feel better. indulge someone means satisfying one's needs.( it is not negative. EG: My mom indulged me with tacos) as to over the top and excessive, the original meaning of over-the-top is "to an excessive degree".So I am gonna say the words are basically the same and can be used interchangeably.