The iPhone 6s and iPhone 6s Plus were released Friday and initial reviews are mostly positive. 

David Pogue of Yahoo says that he can tell the difference in speed between the iPhone 6 and the brand new iPhone 6s. 

"If you operate an iPhone 6 side-by-side with an iPhone 6s, the difference hits you between the eyes. Opening apps, switching apps, processing things -- it all happens faster on the 6s," Pogue said.

The brand new 3D Touch system detects the amount of pressure put on the screen. Quick taps on the screen will display quick previews of items like emails and photos, while long presses will show the full item. John Paczkowski of Buzzfeed has experimented with 3D Touch and is enjoying it.

"I'm already using [3D Touch] constantly, and I am impressed with how good it is at interpreting the force of my touch. It's very much an Apple innovation -- a seemingly subtle change so thoughtfully executed that it proves transformative," Paczowski said.

Joanna Stern of The Wall Street Journal is calling the iPhone 6s "a slightly better version of the iPhone 6." 

"If you have an iPhone 6, you won't be overly jealous of those who get a 6s -- maybe just a tad envious of those Live Photos," Stern said.

Stern recommends buyers upgrade to the 64 GB version of the iPhone 6s.

Matthew Panzarino of Tech Crunch says the camera on the iPhone 6s makes it worth buying.

"But for now, both the iPhone 6s and iPhone 6s Plus are worth your attention and, if it's in your budget, a purchase. The camera alone is worth the price of admission -- it's truly great -- the glimpse into the future of three dimensional computing is just a bonus," Panzarino said.

The iPhone 6s and iPhone 6s Plus went on sale at 8 a.m. local time Friday at Apple Stores and authorized retailers.