What do you think the good average game time is?

I think it's around 32 minutes.

Let's look at it now. If the average game time is 27 minutes (according to Riot), that means we have matches that will span from about 17 minutes to 37. The problem is that the late-game mark is around 35-40 minutes. That's not enough time to get the ball rolling on a late-game champion. On top of that games that end before surrenders are nice and quick but they should NOT be the norm.

However, the likely range on a 32 minute game would be somewhere between 22 and 42 minutes. That means someone who got going at around 35 minutes can take a Baron, get Elder, and use them to close out a game, while someone who got fed 10 minutes in can close out a little after surrenders can be called.

To do this, I think a great place to start is by reducing early snowball potential. Keep first tower blood (maybe nerf it by 100 gold) but fortify bot tower to somewhere between its current strength and optimal tower strength. Increase the damage/tankiness of later towers (preferable inhib and nexus ones) and make ADCs better at taking towers OR APs worse at it, because at the moment a Poppy will outtank a tower (type in "poppy in 2017" and pull up the first Youtube video) while APs shred through them.