The Denny's blog reads as overly contrived to more "hip with the youth" audiences because it is constantly trying way too hard to jump on the latest trends in slang, internet grammar, memes, etc. The complete void of brand values or content on Denny's media presence (as all values have been replaced by eddying internet culture) makes for an unpleasant aftertaste once the original novelty leaves. It just leaves the audience feeling exploited or at the very least patronized. Building a brand voice requires a clear story to tell and "authenticity" (blech, I know) in how you deliver that narrative to audiences. The Denny's online brand has no story other than keeping up with disposable internet ephemera (nihilism is in this year for memes, run with it!) and as a result rings hollow.
Perhaps. But when you consider the platform each targets (Denny's on Tumblr - younger, values visual content. Merriam-Webster on Twitter - older, values witty shortform word) this is excusable.