An important rule is to separate expectative from the show itself. Every show must be evaluated by what it delivers and the marketing has no relation to the final quality. The comparison with Nichijou didn't originate from the studio, so why should we judge this as the new nichijou?. Instead of raising expectations, why not consider it as a new Gabriel Dropout (a good and yet modest anime from the same director)? Shikanoko could never be the next the next Nichijou. There's a considerable time gap between them and Nichijou benefits from certain advantages that Shikanoko lacks.

Good anime tend to to be more appreciated as they age because their memorable moments endure while forgettable ones fade. Aditionally, nostalgia plays a role on how a show is viewed in retrospect. Shikanoko doesn't have any of these advantages. Unlike the classics, it's judged at face value and there aren't many subjective factors that can help it.

So what should I expect from Shikanoko?
From a gag-focused show, it's natural that ome gags work and the ones that don't work must be fun enough to keep the viewer watching until the next one. This is something the classics did masterfully and in the case of Shikanoko, this was done with some relative success. The episodes are funny, entertaining, but never boring, always offering something unusual to keep viewers hooked.

Probably one of the biggest challenges in media production is balancing creative ambition with practical reality. On one hand there is the desire to create something new and groundbreaking, on the other there's the need to appeal to audiences to survive in a competitive industry. The prevailing force directly influences the final product.
The most innovative episodes were directed by Masahiko Oota, a veteran of this type of comedy, with animes like Minami-ke and Gabriel Dropout under his belt. It's no coincidence that two of the best episodes were directed or written by him. Certainly he was the person behind the brilliant moments.
However, other episodes suffered from inconsistent quality. In these episodes, the creative side seemed to falter, leading to generic comedy. Lack of inventiveness and boldness hindered Shikanoko from reaching its full potential.
Of course, this alone doesn't make an anime bad. Even Nichijou or Lucky Star didn't always hit the mark. In any show, especially those built around gags, some will inevitably fall flat, but even these moments serve a purpose. Introducing characters solely through gags would be challenging, so slowing down or even fail is sometimes necessary.

The characters were typical anime archetypes, which isn't necessarily bad. Many shows follow this approach. While a bit more variety would have been nice, the main duo had his moments. I was particularly interested in the dynamic between Anko and Meme, but it wasn't explored as much as I would have liked.

FInal thought:
Shikanoko never aimed to reinvent the wheel or make history. It's a fun and silly show that should be appreciated for what it is. Keep your expectations low, and I'm sure you'll enjoy it as much as I did.