The worst effect of IAPs is that a lot of games are now basically just a wrapper around the IAPs. Just a way to poke and prod you into dumping some money.
One of the worst recent examples I played was the new Angry Birds racing game, Angry Birds Go. It’s tragic, because the game LOOKS great and the racing physics feel pretty nice. But there’s no real game there – it’s pretty clear pretty quickly that the “racing” is pretty much just a case of buying the best accessories for your cart and winning. If your car isn’t properly upgraded, you can’t win even if you play perfectly. If you ARE upgraded fully, you can win races without looking at the screen.
It could have been a fun game, but it’s clear that Rovio wasn’t trying to make a racing game, they were trying to make a purchase pump. Wasted opportunity, wasted time.