Why don't we make a shehecheyanu blessing on counting the Omer? It is a mitzvah which we get to do after a very long break (more than 300 days)?
Some arguments I have heard:
- In a similar situation we make a shehecheyanu on the lulav
- Perhaps Purim could serve as a counter-example - we make a shehecheyanu on reading the Megillah to include all other commandments of the day - so maybe here it's similar. But you usually count for the first time before kiddush, where we make our shehecheyanu. And also mitzvos of Purim day have no independent blessing...