I posted an earlier comment before the game was released. Now that I've had a chance to try it out, I must say I'm disappointed. The IAP alone aren't the only annoyance. The game just doesn't have the same charm as the original. Since none of the original folk who worked on the first game were involved in this one, the difference is quite noticeable:
The music is blah. I LOVED the music in the first game. This one, I'd rather turn the sound off as the music is just bland. None of the new tunes are catchy or enjoyable to listen to. The voices, same deal. The zombie voices are ear-piercingly annoying. I don't like using the power ups. I find them little-more than cheats and makes the game too easy.
And finally, the only annoying aspect of the IAP is that you can't take the slow route and use your coins to unlock things. They should've done like in Real Racing 2 where you're given the choice of either unlocking right away with real money or taking the slow route and use in-game currency instead. Here, you're not given the choice. You HAVE to use money instead, rendering the in-game currency worthless. (except to buying power ups which I'd rather not use anyway) You aren't given a choice. Perhaps this would be addressed in a future update where you're given a choice between paying with real money or in-game currency, but I doubt it.
I've yet to reach the point of needing to collect many stars to unlock the next stage but I read about it here and that just seems like an artificial way of making the game drag on.... and I'm already bored as it is. I can't imagine how boring it'll get if I'm forced to repeat a level several times.
So, while I was right about reserving judgement till the game came out (I kinda had hope since RR2 is actually a good game despite the IAP), not anymore. This game sucks and I'm incredibly disappointed.