I think it's up to Apple to somehow provide clarity in the Appstore about the extent of IAP. Right now I have to do additional research to get an idea of how much of it offers actual gameplay and I usually can't be bothered to do so.
Most of the time I'll wait for IAP games to drop to free and then choose to buy some IAP or the sequel if I think the game is great to make up for that. I make a conscious effort not to get games without gameplay-related IAP while they're free, but I'd rather try them first.
My ideal model for games that aren't little timewasters is offering a free demo like The Room or Ace Patrol, the rest of the core game via one IAP and additional IAP to rip off losers through cheats & skins.
Can we classify IAP? What do we have now:
1. No IAP
2. IAP to unlock game related items (new weapons, lives etc)
3. IAP to skip barriers (remove cool downs or save the gamer from a lengthy repetitive task).
4. IAP to unlock
additional content (with the emphasis on additional, such as new maps or scenarios or modes).
5. IAP to unlock cosmetic details (costumes, skins).
For me, I draw a distinction between 2 and 3 because 2 is making you pay for something that is theoretically integrated into the balance of the game and 3 is making you pay for an artificially constructed barrier.
Anything missing from that list? An IAP that permitted you to extend your run would probably fall under #3 if there was no way to earn such abilities naturally, or #2 if you could.
Given that list, I have generally been happy with #1, #4 and #5. #2 is a difficult one because it is all about the balance of if you can achieve things with regular play. #3 is an instant turn off (and poorly implemented #2 features tend to drift into here).
The App Store is great, the IAPs are starting to get out of hand though. It's starting to devalue the newly released games for me and I have been buying and downloading less as a result. I know I'm just one voice but to me it's important, maybe I'm just old school but I'm sure I'm not the only one who feels this way.
It is an evolving thing. For me though the far bigger problem at the moment is games being heavily discounted like two days after release. It makes me want to never pay for a full price title and I think this has to be skewing the industries perception of what models they should be using in some way. Of course $9.99 games will not sell if everybody knows they will be $0.99 in a week.