Nah it should be relatively short so it leaves people wanting more. One good way to do this is when they show the traditional montage or whatever show some really cool bits of some games but don't talk about them AT ALL. I remember when I saw Gravity Rush on the vita reel I was like ''What game is THAT!?''. Then slowly start to give info on the games you didn't focus on the event leading up to E3 where you blow people away with bunch of new unannounced games.
Show 2 first party games that you are confident in-depht developer real time gameplay/commentary and all that cool stuff. Stuff that isn't quite ready you put on the reel for a nice tease
. Third parties handle the rest.