Google Wallet is like Apple Pay. The only difference being Google Wallet uses a virtual debit card in order to mask and protect the user's financial data, while Apple Pay uses one-time authorization tokens.
No, that's not entirely accurate.
You fund your Google Wallet with either a credit card (if you're smart) or your bank account (if you're dumb).
When you pay with Google Wallet, Google pays the merchant through MasterCard, and then charges you that amount.
So there are a few differences:
1. Google maintains your financial information. If they get hacked, all Wallet customers are at risk. With Apple Pay, your issuing bank holds it, and compromise of one bank only affects that bank's customers.
2. Any programs you belong to that link purchases made with your credit card to rewards like uPromise and Fuel Rewards Network won't work, since they never see your card being used.
3. Google sees what you bought, where you bought it, and most likely either sells that data or uses it for more targeted ads - which may offend some folks from a privacy perspective.
4. There were (and still might be - I don't know - anyone?) handset and carrier restrictions on who could even use Google Wallet on the Android side.
I haven't looked into how secure Wallet might be from a tokenization perspective, but I presume it's well thought out; Google is pretty good with security.
Both, of course, are likely much better than swiping your card, using an EMV/Chip & Pin card, or - God help you - CurrentC.