If you're creating an actual, informational web page, stick to frameless HTML, CSS and unobstrusive JavaScripts and keep in mind that the page should still be usable with scripting disabled.

First, the frame and frameset elements are not deprecated in HTML5, they're obsolete (i.e., they've been removed entirely).

but I wouldn't use a frameset for anything but a manual since it no longer exists in html5. Example: Game maker manual

Designers hated them. Yes, that was the deadliest punch. Everything looked square and straight. They hated it. They wanted arcs and image backgrounds and rounded borders. Now they have it in CSS3 - guess what, they're drawing squares. #whatever Programmers had trouble with them. It was inconvenient to follow the logic of frames, and you had to do some extra work. I mean, some. Today it's a lot harder to create AJAX solutions for the same problem, but no one complains. #whatever Websites could include one another. This was painful for some site owners because they worked hard on something and another fella used it as own content. Later, they invented same origin policy, but it was way after starting to hate frames. Content stealing is still an issue today, absolutely unrelated to whether we have frames or not. #whatever Back button worked differently. Yes, it was a bit annoying. But it was not the frame concept's fault, again: it was browsers who did this to us. Could have been solved easily, but nah, browsers kept going back one by one, not providing the site a way to implement its own "step back" method, and alas, this is still happening today. #whatever