No, it’s not an interstitial – but almost. Have you ever measured the dwell time on a social networking portal entry page? Not much, especially not if you are a frequent visitor. Your focus is on typing your password correctly – and after hitting enter that’s it, you are in and entry page is gone.
Now, you may play around with the message reflecting on the only activity you do on an entry page and that may grab the visitor’s attention but placing any contextless game there is a waste of money. Lot of money. Next time, don’t just buy a very remarkable and expensive ad space, take the time and think about what you are placing there.