Sure there are a lot of good books created by good authors, but if you're looking for fan fictions (every fandom except for real life), go to fanfiction.net or archiveofourown, because you won't find any good ones there. Basically, the fan fiction side is almost all written by middle and/or high schoolers.
While fanfiction.net offers a filter able to show you the lists from update date, upload date, favourites, follows, completes, incompletes, able to choose two genres, how many words you want in the story, or even discarding options, you can get a more precise search. Whereas wattpad doesn't. Furthermore, fanfiction.net allows authors to shine more easily (at least in my case) in that particular fandom.
Upon searching hours and hours, days upon days, I've only found five rare gems hidden from view.
The search engine doesn't work as you'd want it to, because you'll never find the kind of book you'd want to read. Besides that, there's no filters (except for looking for 'complete stories) to narrow down.
So in terms of the search engine, I think they could improve.