I must admit:

I’ve not been a fan of Windows for quite a few years now.
Especially when I started using a Macbook Pro as my main computer end 2012. I practically use it as a desktop when at my home office: external flatscreen monitor, wireless keyboard and mouse.
On my left is my ‘old’ Windows desktop with a flatscreen. I use primarily for testing sites on Explorer and displaying Google analytics now.
When the first Windows 10 Insider Preview edition came out, I figured: there is no data that isn’t backed-up or that can’t be missed on this system, why not install the preview (I could always fall back to the W7 that was  originally on it).
In fact, the process was rather painless, it took a while, but since this is not my primary system, it was no big deal.
Once installed, I was quite amazed, this system actually beat the Macbook in startup time (although the Macbook I usually just put to sleep).
But for the first time in years I was actually impressed with Windows. OK, there have been regular (again rather slow) updates over time, but I was warned for that. 
Back in Januari, the next big surprise coming from MS was the pretty amazing Hololens announcement.
Although the on-stage demo must have been kind of awkward for the audience (they did not see any of the VR/AR attributes on stage), the demo movies were in fact amazing.
But more on that later.
Now with the Build event (April 29th-May 1st) things have materialized some more. On the part of Windows 10 there are indeed some thing worth noticing:
The same W10 Apps can be used on phone, tablet and Desktop, provided all devices run W10.
Apps behave and scale differently on different devices, but share the same code-base.
Being able to run Excel from a W10 enabled phone with an external monitor, mouse and keyboard and offering a Desktop experience (although probably a bit slower) is pretty neat.
This is in fact pretty significant for App developers, sincethe codebase can be kept smaller.
Speaking of code base: the announcement of support for Objective-C (mainly known for iOS development) in Visual Studio. 
That is a pretty big thing as well and a smart move for MS: get a new potential group of developers involved in writing / porting their apps. 
But, to the laymen it might sound that porting an iOS App to a W10 phone is now a piece of cake, but I’ll question that. 
What the presentation did not mention is whether the SDK core API’s (how the programmer ‘talks' to hardware and system devices) are also supported. In theory this actually would be possible by wrapping W10 phone API’s in wrappers that mimic behavior of other platforms, but knowing the amount of work involved, I doubt this is the case.
In practice this means that the basic code constructs can be used on this platform, but interfaces that require device specific code still have to be rewritten.
When thinking of the iOS App I made that involves the OpenGLES, CoreMotion, CoreVideo and other API’s that are quite hardware related, I doubt the code can be ported ‘as is’ without major adaption or redesign.
But then the grand finale, after januari’s first impressions of hololens, the Build audience now got a much better look at what this really encompasses. 
Although it was practically not possible to provide the audience with exactly the same experience as the wearer of the hololens, the camera setup at the build event provided a reasonable impression of what to expect.

And what to expect is actually pretty awesome. If Hololens performs as well as depicted, it provides the best out of two worlds: AR and VR combined.
MS seems pretty confident: invites for trying an actual hololens for the attendents of the conference
On installing the Windows 10 preview
One word of advice on Installing the W10 preview: Download a fresh copy.
I made the mistake of using the same ISO image I’d used earlier for my desktop PC (~2 months ago?) to install it on a laptop (while watching the Build conference video).
Because this was an old, now expired build, it complained. I thought, it will get updates, perhaps repeatedly until it is up to date, but no.. In fact at one moment the laptop seemed fried.
The only way to get it running was with a freshly downloaded ISO, so be warned.