Yes, both the iPhone 6 and the iPhone 6 plus have Siri and it's very useful for asking intelligent questions, such as weather forecasts and sports results but when you get bored it's fun to try to annoy Siri too...
With iOS8 comes the ability to talk to Siri hands free if the phone is turned on and charging. I use my phone as my alarm clock, so I just turn off my notification sounds and leave it on all night. It's quite useful to wake up in the dark and say "Hey Siri, what's the time?" and get an immediate answer.
I also like to question him about the weather when I wake too, so that I can plan what to wear before I leave my warm bed.
Siri is also useful when I am busy. I was writing Christmas cards at the weekend and a friend kept texting me. Luckily it was just one button press to get Siri to read my messages and answer them for me, he's a star!
I'm looking forward to using Siri on the Apple Watch, I think he will be very useful on that too.