While the iPhone 7 introduces some new technologies, it has offered no significant improvement over the iPhone 6s. If you own an iPhone 6, the upgrade might not be worth it.
The iPhone 7 looks very similar to the iPhone 6 plus with very few differences that aren't that noticeable. People who buy iPhones to differentiate themselves might not find iPhone 7 worth it. See why some people love iPhones.
The iPhone 7 has a poor battery life compared to that of the iPhone 6S. According to The Guardian, the phone's battery lasts for 14 hours when heavily used and takes a long time to charge.
The iPhone 7 has no headphone jack. A person must buy an adapter in order to be able to use their old headphones. The iPhone 7 is also not fully compatible with wireless headphones made by other manufacturers.
Some people believe that the iPhone 8 will be significantly different from the iPhone 7. For iPhone 6 owners, it might make more sense to wait for the iPhone 8. See also why iPhones break so easily.
Many reviewers said that the changes from iPhone 6s to iPhone 7 are good but not really worth an upgrade. Among those changes are an improved camera, water resistant feature and a better processor.
The iPhone 7 starts at 32GB of storage and so it's more expensive than the iPhone 6s. The iPhone 7 might not be worth the upgrade if you already have an iPhone 6.
Apart from slight performance changes and other minor features, the iPhone 7 offers no innovative upgrades. It's not a next generation phone, and as a result, it's not that different from the iPhone 6.