I'd be curious to know what prompted this retirement. Having moved from Google Checkout to Google Wallet, it's more than a little frustratingt. The Wallet customer experience was pretty good and the integration process was fairly simple. It's a shame to lose this and lose yet more faith in Google to keep their services alive.
I get zero chargebacks via Google and struggle to find anything that's comparable?
I've got the usual horror story behind PayPal (that cost a lot) and Stripe does not have adequate anti-fraud.
At the moment Amazon Payments seems to be a worthwhile competitor (they guarantee no chargebacks related to fraud) however their service is much harder to integrate. Although plenty of humans in the mix which is a very nice touch.
As a merchant, this is why Bitcoin is so valuable.
Google was handy because their policies weren't overly restrictive - perhaps this is what sunk the digital goods api... Stripe is wonderfully easy to set up but doesn't allow integration for certain types of app e.g. telecoms (I understand that this is because of retrictions banks have placed on them).
Trustworthy Bitcoin payment processors are tricky to find. The stripe approach to this does give the lowest amount of customer friction imo (i.e. options to convert usd to btc on the spot) but the market restrictions and the beta status make it a non starter for now.