Did you like Peter Abrahams "Down the Rabbit Hole", Echo Falls mysteries? Then, I think you will like "Sweetness..." Flavia de Luce is very similar to Ingrid. Both are persistent, intelligent, curious yet childish and endearing. Both end up in loads of trouble and both try to right wrongs.
It's definitely geared towards younger readers, but still intelligent enough for mature ones. I found her interest in chemistry quirky, and her thought process the same... The only thing I didn't like were some of the unusual references to local pop culture. If you aren't familiar with local rural, 1940's 50's English culture, you won't get some of the references. I didn't. I almost googled them , but in the end they didn't really play an important part in the story, so, I thought, why include them at all?
I don't think I would run right out and buy the 2nd and 3rd books... but, if I see them at a good price, they're a fun read.