Katanagatari is interesting because it's one of the better anime in recent time (that I have seen), one of the best anime from 2010 (that I have seen) and arguably the best work of NisiOisiN (that I have seen, even though this only includes two titles).
Now, Katanagatari is great, it's absolutely wonderful, but depending on your ability to immerse yourself in a story so much that you forget time this may or may not be for you. If you are like me with the attention span of a goldfish, initially the 50-minute long episodes might scare you off. If you are able to put up with it, however, you are in for a treat.
I will not summarize the series because frankly you can look at the anime description for that, that and I doubt I will make it that much more interesting. I will just go through why I like it.
First of all there are the characters, which I think are the main driving force behind this anime. They bounce off each other really well, providing good (but not ROFLOL hilarious) comedy and creating an overall likable character dynamic. The side characters are also fairly good, they do their thing, but for the most part you will not see them for more than one episode, so they do not matter too much. I will also give points to the incredibly forced romance. I like that Katanagatari doesn't even try to build it up naturally but instead approaches it like "Yeah, we're in love even though we've shared a whole of five minutes of screen time. Deal with it." The action scenes are short but very energetic and well directed. While they are very good, be warned if you are going into Katana thinking it will be 90% action; it will not. In fact, much of the anime is spent on dialogue. Think Bakemonogatari, just not quite the same bullet pace.
The sound track is excellent, and while I do not think it stands out per se the music tracks are used very efficiently, creating just the right mood every single time.
The art can be described as fairly minimalistic - it certainly does not stand out in terms of production values - but it gets its job done and does it well.
Overall, Katanagatari is great, you should definitely check it out if you like dialogue and good action scenes, but due to the length of the episodes you may or may not be able to marathon through it. Also: that last episode.
