If you've ever seen any offerings of xxxHOLiC you should know what to expect from xxxHOLiC Shunmuki.
In xxxHOLiC Shunmuki the quirky art style presented in the other xxxHOLiC series remains unchanged. Additionally, when compared to many of the newer higher resolution series xxxHOLiC Shunmuki seems inferior, presented in the lower resolution format, reminiscent of the original series. Visually, xxxHOLiC Shunmuki's offerings are subpart and vastly inferior to many of Production I.G.'s other offerings, possessing nothing more than mediocre animation with a gimmicky art style.
As for the actual episodes themselves they don't offer very much in terms of plot or character development and feel more like filler. Luckily, it's far above the level of the downright-awful fillers of shows like Bleach and Naruto.
While xxxHOLiC Shunmuki is certainly nothing to write home about and is wrought by mediocrity it still manages to be moderately enjoyable. Although not particularly noteworthy and nothing I'd recommend, it's not bad if you're looking to kill some time.