When a new flagship phone lands, one thing always crosses our mind. Is it really worth upgrading? The only way to find out is to look at the features of both head to head.On the face of it, there isn't a huge step up here with the Sony Xperia Z2. After all, the Xperia Z1 was only launched late last year and was highly rated by us in review. In terms of design, they don't look a million miles apart, with the Z2 just a little lighter and slimmer, and perhaps a touch longer with a display up by 0.2 inches. But the design has barely changed - right down to the colours being offered of black, white and purple. With that in mind, there's little to differentiate.But beyond the design, things have taken a step up. That screen is now a TRILUMINOS display and with Live Colour LED, offering colours as natural as the ones you see with your naked eye. No resolution change, but a better display than the Z1 for sure. Sound should be better too with the addition of front speakers (rather than rear), while the use of Sony's digital noise cancelling technology should be useful if you want to block out the world on a long trip.The camera doesn't look to have changed much from Z1 to Z2, but Sony has thrown in a number of whistles and bells to make photography more interesting. The latest phone gives you the option to shoot video in 4K (four times the detail of full HD), along with the new Movie Creator software, allowing you to edit the videos before they go 'live'. There's also Timeshift video (for shooting in 120 frames per second), creative effect, background defocus (which simulates a shallow depth of field), AR effect for augmented reality animations and Twitter's Vine app pre-loaded. So a similar camera, but a lot more you can do with it.Of course, a key difference here is Android 4.4 KitKat on the Z2 and all that the OS offers, something the Z1 has yet to experience (but will do eventually). That should make things a little speedier too, as should a 2.3GHz quad-core Snapdragon 801 processor (there was a Snapdragon 800 in the original) and 3GB RAM (2GB on the Z1). A stronger battery too, with a jump from 3000mAh to 3200mAh from Z1 to Z2, but the same storage options of 16GB, both of which can be increased via the microSD slot.So overall, we're looking at evolution rather than revolution, with Sony really just bumping things up across the board. With the original phone only around six months old, that's no surprise. But if you were looking at the two head to head, the Z2 is definitely the more appealing option. Although much will depend on the price being asked by the networks. If the Z1 gets an upgrade to Android 4.4 and a hefty price cut, we might reconsider our view.