The iPhone's mail app is fine, but it's got nothing on the functionality of the full Gmail setup. And Google's mobile Gmail site is great, but it can't work fully integrated into iOS with notifications and such. For that, they'd need a native app. And at long last, one may be coming.
Apparently, Google has recently submitted the app to Apple for review, which means it could hit the App Store any day now. So you'll finally get the full Gmail experience, with the priority inbox, labels and stars, right on the iPhone, with Notification Center support and push notification. What took so long? Who knows, but hopefully the long wait will be over soon.
Via Paris Lemon