DESIGN
There's really no getting around it: the iPhone 7 and 7 Plus look more or less exactly like the iPhone 6 and 6 Plus from 2014. They are now water resistant, which is nice, although they're not fully waterproof - keep them submerged in a meter of water for more than 30 minutes and things might not go your way. Samsung's Galaxy S7 and Note 7 are technically even more water resistant, but I think it's basically a push - you can get these phones casually wet now without catastrophe, and that's a big win. If you want to go snorkeling with your iPhone, you should probably get a case anyhow.
Apart from the water resistance, there are three main external differences between the 6 and 7: first, the antenna lines on the back have been tweaked and colored to blend into the body on the matte black and glossy jet black models, which is a welcome refinement. (The antennas remain a dull gray color on the silver, gold, and rose gold variants; Apple says there are limits on what colors can be applied.) Second, the camera bump has been enlarged and more artfully curved into the rear casing, which looks particularly handsome on the smaller phone with a single camera.