This blog provides in-depth explanations of some grammar and vocabulary topics in Mandarin Chinese. While there aren't a huge number of articles so far, there are enough to issue a general recommendation. Apart from some Chengyu explanations which I find of moderate interest myself, there are some really good posts, such as:

• Characters Indicating People: 师, 生, 员, 家, 者 and 人
• What is the difference between 怕，害怕，恐怕，可怕，恐怖 and 恐惧?
• What are 形容词? Are They ‘Adjectives’ or ‘Adjectival Stative Verbs’?

Note that you shoudn't really use a resource like this to study new words. For example, if you've never seen most of the words in the second article mentioned above, you haven't listened or read enough to benefit fully from such an article. You need exposure and a passive sense of what things mean before it's wortwhile to really study differences between them.