@ LPChip: I considered sideways text, but it wasn't appealing in my mind. I'll see how it looks, and maybe post it for public opinion. I think the purpose of the brackets is self explanatory since they're selected by default when the selection menu starts.
@ Salmoneous: A search bar is a great idea. I envision treating all entries as if they have wildcards at both ends. Then, matching that to title, author, folder name, and description all at once. It begs the question, where can I put it. I could stick it at the top of the filter panel if I get rid of "Last Installed"*, but I'll have to reduce padding further. I could put it below the level blocks next to the page buttons. Hmm... I just don't know. I really want to add a search bar now! It would be so helpful!
*I haven't mentioned this yet, but "Last Installed" is an unimportant filter because when you install a level a link to that level appears in the installation menu (see image.)
@ SergioCornaga: Although check boxes are a viable alternative to an "all" button, I think they would be tiresome. A way to turn them all on or narrow down to a single flavor is necessary, but clicking on the words is non-intuitive.
Edit: The search box is complete. Everything works great as far as I know. Although it's looking good, I'm not satisfied. I have no idea how to improve the layout again. I've added images of the current layout and a mock up of LPChip's suggestion for the filter bar. So, please voice your opinions, suggestions, etc. for the ideal layout.