Depends what you want to get out of them. I find some are mostly focused around some of the more unique/cool challenges they come across (Google[1][2], Slack[3]), and others are more about how they solve the engineering challenges they face through software and/or about their dev process (Uber[4], Twitter[5]). Some are mix of the two (Dropbox[6], Netflix[7]).
[1] https://developers.googleblog.com/
[2] http://research.googleblog.com/