It can be hard to pack a lot of content into a single Web page, but that's what good navigation is for. If your site content generates a horizontal scrollbar in a browser window of reasonable size, rethink your layout. While most new laptops come with multitouch trackpads that permit horizontal scrolling with two fingers, not all do, and many people still browse the Web on desktops with mice that only scroll vertically. Horizontal scrolling is a hassle, and it's not something that people look for, so visitors may miss content on the sides. Try to rework your layout to include a deeper menu structure to accommodate all of your content, and make sure it scales properly to fit a narrower browser window.
I think Denny’s was going for the feel of a paper menu with the layout of its website, but it just looks cluttered. Also, the animations used for sliding to the next side panel are slow and laggy. I shouldn't have to wait for content to scroll onto the screen, and jerky animations don't look good.