This code, once added to your child themes functions file, displays the full content for the first post on both your blog & home pages, then excerpts for all other posts.
The code includes the is_home & is_page_template conditional tags you can modify or remove to suite you own needs.
You can use this code to show full content on the first post on any type of archive and the excerpts for all other posts in the archive. You can also determine the word limit for the excerpts.
The code has been tested on the Genesis Sample child theme by StudioPress.
Here’s the code: