Gmail isn't great on any Android device. If you have only used Android, it might seem great. But after you try the built-in iOS client, your standards will raise a bit (not intending to offend!).
In my experience, nothing that Google has produced for the mobile platform(s) is great.
Seriously? You think the iOS mail client is better than the Android Gmail client? Because... it just isn't. For me, anyway. Each to their own.
Of course Google has made great things for mobile. Maps are unparalleled. Google Now is fantastic. The Google+ apps are actually fantastic, it's just that no-one is using them.
Gmail isn't great on any Android device. If you have only used Android, it might seem great. But after you try the built-in iOS client, your standards will raise a bit (not intending to offend!).
In my experience, nothing that Google has produced for the mobile platform(s) is great.