Apple is rolling out iOS 8 in time for the release of iPhone 6 and iPhone 6 Plus this week, but critics say that there is not much of a change except for some useful system tweaks that improve the devices' user friendliness.

In terms of the design, Independent UK reported that iOS 8 is following the footsteps of its predecessor by retaining the non-skeumorphic design and sticking to the flat, vividly-colored interface.

Users who also make good use of Siri can now do voice commands hands-free as long as the command keyword is within a reasonable distance. Apple also reinvented how Siri receives instructions using real-time visual typing so users do not need to wait until the command is finished.

With the public sale of iWatch in early 2015, Apple's health app becomes one of the most powerful programs to track, record, and analyze statistics of the user. In iPhone 5s, users have to manually input data before the app can be useful, but with the use of Apple's signature watch, all information is synced in real time. The downside is that the Health app cannot be maximized without the accessory device.

BGR, a tech review website, also noted that iOS 8 allows third-party developers to improve functionality on iPhone users by using widgets. This makes iPhone 5s, iPhone 6, and iPhone 6 Plus all the more user-friendly without sacrificing battery life and system performance.

Interactive notifications are also a big advantage in making the most out of Apple devices' multitasking ability. For example, users can still send a text reply while typing an e-mail message by dragging the text notification to the bottom part of the screen, and then return to sending an e-mail.

The iOS 8 update is available starting Wednesday for iPhone and iPad users free of charge while the iPhone 6 and iPhone 6 Plus will be released on Friday, September 19.