Whatever the content is make sure that the subject line goes well with the purpose of your content. Subject line plays important role in open rates, however as most of us receive too much of junk in our email inbox, we have developed this tendency identifying the spammy subject lines in most of the cases, and deleting of such emails straightaway without giving it the second look.
The behavior of the recipients shifted from highly salesy subject line to straightforward subject lines. Subject lines that place excessive emphasis on selling what is inside the email are falling short in terms of open rates. Try to use straightforward subject lines without being salesy.