there are a few recipies there so I don't know which one you are referring to, but I can still make some suggestions...
I make quickie salsa (in the winter when there's no fresh tomatpes) with a can of diced tomatoes, a couple of chopped onions, a ton of garlic (I like to use fresh AND powdered just to be sure) hot pepper (I like habaneroes but you only need one, jalapenos you can go nuts with 'em) and add a mix of spices (I like to keep 'em whole and grind them up when I need them) usually including: cumin seeds (can't go wrong) black pepper, some coriander seeds, a dash of fennel seeds and some fresh herbs like oregano, basil and summer savoury. Add juice from one or two limes, salt and pepper to taste then mix it up with a spoon and let it "marry" for as long as you like- if you use regular yellow onions you hsould leave it longer, if you used sweet onions, you can eay it sooner.... some canned corn can go in there too, if ya like, but definitely give fresh-ground cumin a shot, it really works well I find
EDIT- okay, I chercked out a few more of the recipies- looks like lime juice could be the key, and I would maybe suggest leaving out the white sugar, and boosting the cumin content of the first recipie (and adding the other spices I listed) and you should have your proper salsa
Fresh cilantro/coriander leaves might help too, they have a sort of peculiar taste tho, I have a feeling they are a love/hate taste so if you try them proceed with caution