mobile

I have a few questions and I would really appreciate if you could answer it honestly. So, I have the M8, and I love it. Now, I'm considering M9, and here's why:
- Sense - not mainly because of it's looks or features, but for optimization. It's smooth, no lag, and most important, no problems at all. And I really mean it.
I had a phone for a year now, and it didn't reboot itself or crashed in any way, not even once (my up-time is usually more than 2000 hours, before update comes) Not even for a second. It's amazing how reliable it is.
- HTC support and updates - I love how they keep their apps on the Play Store and update them constantly, I love how they randomly push an update with additional features.
And I love how I will be able to update to Sense 7 with all it's features on my older model.
- build quality - I love metal phones (I also loved glass on my Nexus 4), I love the feeling of sturdiness and quality and I love that the phone is well put together.

Now, to the questions - I love technology and everything that goes with it, that's why I really like the new S6. So, by never owning a Galaxy device (except Nexus),
I don't have much experience, and that's why I would like to know:

- how is Touchwiz with the S6? I know that the phone is still relatively new and most of you didn't use it enough yet, but does it still has the problems that previous models were known for (lagging, reboots, etc.) - I know reviews say that those problems are gone, but still.
- how is Samsung with the updates - i.e. will my S6 be updated with the features that S7 will bring? Does Samsung cares about updates and improvement once they sell the phone?
- build quality is the one thing I believe in, so I hope I'm not wrong. :)

This is basically all that I wanted to know. I just afraid to dive into this new phone just because it looks (and is) like a total beast. I just know that I will instantly forget
about that beautiful screen if the phone will fail on me, reboot randomly, lag... so I just want to be sure. Also, it would suck that a year from now, Sammy would bring new features with the S7 and
my S6 would be forgotten, left in the dust. Also, you can add anything that you thing may be important in this matter. So, thank you for you (hopefully) honest answers.