There have been questions about the reward tiers so here's an update to clarify.
The rewards should have been explained that all tiers $15 and higher include digital copies of the previous 3 games. All tiers $20 and higher include a digital copy of the game soundtrack and the three previous games. All tiers $30 and higher include the concept art and certificate of diagnosis, the soundtrack and previous three games. The $50, $100 and $150 tier include what's specified plus the concept art, certificate of diagnosis, soundtrack and previous three games.
I'm sorry for the confusion. I tried to present the rewards in a simpler format and it kinda backfired. I'll work on an image of all rewards to better illustrate which rewards are with what tier.