According to NeoGAF it has been confirmed that the event is in fact annual http://www.neogaf.com/forum/showthread.php?t=947296

I'm expecting what everyone seems to expect: Drawn to Death

Druckman photobomb XD

http://www.neogaf.com/forum/showthread.php?t=947203

I'd love it if it was Horizon.

There likely isn't a super secret game anymore. They just couldn't name it on the schedule list ahead of the keynote. It's likely a game that was already announced at the keynote. So I wouldn't expect any surprises..

Yea. Prbly Drawn to Death. Or Killstrain.

Sunset Overdrive Sigma ;)

The mystery game is Shovel Knight

Our next live #PSExperience demo: Shovel Knight on PS4 with @YachtClubGames! Watch live: http://t.co/kC0oVa15HR pic.twitter.com/DSJUq4UDtm

— PlayStation (@PlayStation) December 7, 2014

Edit: live now

Nothing against Shovel Knight, but I hope not, I'm hoping they're just doing a little bit of gameplay for that and then they'll show a bigger surprize. If it's only Shovel Knight then I'll go back to playing Plants vs Zombies.

Well Shover Knight isn't in the schedule and was announced at the event, so it would make sense if it's the mystery game.

Also, PvZ is damn fun!

Im so confused?? I tuned in to see Shovel Knight??
We knew about this already, Im buying it day 1, if I want to know about it I can watch a fucking lets play or Caddie's new vid because its already out on 3 platforms. Why is it being shown now -_-