There is no negative button, a user "likes"/"thanks" a post, that's ultimately it. If you find it useful, "like" or "thank" the post, you can remove your existing "like" only, you cannot downvote. If you "like" a post, then a +1 is given to the users profile field "likes", if you remove your existing like, it decreases the amount of likes (as it's only increased when a post of theirs is found helpful).
Basically it keeps track of how valuable a users content is. You can rename "Like"/"Unlike" to whatever you want ("Kudo's", "Likes", "Thanks", it's all in the language files.
And it's not over-engineered. It does what it should do for being able to "like" a post on any other forum title, only it keeps track of how many times a user has had their posts liked.
