+1 They're hell bent on making a single (or as similar as possible) for phones and PCs and it obviously has to cater to the lowest denominator. Result: The desktop loses the highly polished interface that has evolved over decades. I hate it. The funny thing is, I thought that if anybody, it'd be Apple who would do this (because they're so oriented to simplicity) but they have enough sense to keep the UI for PCs separate from that of tables and phones.

But the price to pay is a worse mouse experice :(

Many of the applications included in Windows have been rewritten with touch optimized ("modern") UIs and that leads to low information density and waste of screen real estate.
The problem is they're trying to make a single UI to be used with fingers and a mouse and keyboard and that's really difficult without making a substandard UI for any (or both) of the paradigms. I use Windows on a desktop computer and Windows 10 should not penalize me for it. I have a mouse that's capable of very precise movements and I want an UI that makes the most of it, just like they used to be. I want lots of buttons and relatively small text. That's impossible for a single UI for both touch and mouse use.
IMO they should make 2 different UIs for each application (all the logic can be easily reused) but today desktops seem to passe.

You're up to +5 already but I'll just say that I totally agree. I wouldn't mind the ugly touch UI and "apps" if there was a switch to change it all to "classic" desktop mode (i.e. Win 95 to 7).
What's wrong?

• Horrid usability for desktop use (everything flat with no hints as to what's clickable, tons of waste of screen real estate because there's so much whitespace in apps)
• Most programs have been rewritten for touch and that means : Tons of whitespace leading to waste of screen real estate, low information density
• You're pushed to use Microsoft services: Bing, OneDrive (can't be uninstalled), Windows Store, Cortana...
• The start menu is back... but is very limited compared to Windows 7's
• Configuration split between a "modern" app and the classic Control Panel

Which is unforgivable since consoles are PCs are more alike than ever. It should be much easier in this generation to port between systems

After a 50$ CPU was able to run Office and your browser with room to spare, Intel and AMD needed more resource-hungry software to make people buy new CPUs, and what better than the most used piece of software in offices around the world, i.e.: Minesweeper :).
On a more serious note, they also used its popularity to get people accustomed to using the Windows Store (in Win 10 you must install it from there or no Minesweeper or other Microsoft games for you).

Youi're missing the point: This is not being added because people use Cortana much (Win 10 hasn't even been released yet!) but it's another strategy to get you to use it more.
Microsoft has done many things in Win 10 to tempt you to use their services (e.g.: search searches the web by default using Bing, OneDrive can't be uninstalled,..) and I hate it

+1. I'd also pay money to Google to be able to use Android without any of their apps (i.e.:being able to uninstall those I don't use).
I'd also pay money to Microsoft for a Windows 10 without any of their services (Bing, Onedrive, Store, Cortana)

No, all are the same thing: a means to get more money.
The difference is that Windows didn't use to have it and now does, and moving solitare to the store isn't done for technical reasons but for forcing you to use the store

Yeah, DirectX 12 is the only reason I see to upgrade. And it irks me to no end the fact that I'll have to use a OS worse than Win7 (IMO) to get it

Yeah, it's a political removal. The only reason to do this is to force people to go to the Store to download it and get them used to get "apps" of which any sales Microsoft will keep a 30% cut

Hey, don't complain!, it's for your own *cough Microsoft's *cough benefit ;)

I read somewhere that, while developing Windows 8, it was found in internal testing that most people hated the Metro interface. They kept it anyway.
The takeaway is that they did test and tests were negative but they went on for business reasons.
They want you to get used to the metro UI so that you'll get used to it and you'll buy a Windows Phone phone. Also so that you buy metro apps through their store and they get a 30% cut, so that you use their services and they get your data and money , etc.
TL;DR: They know it sucks but they want the money they think it'll make them

Exactly! Seems like the motto is :"One true,flat,ugly way".

+1000. I completely hate the modern UIs made to be usable on anything. They're jack of all trades master of none, and of course, less optimal for desktop use that the previous ones which were tailored for them.
Now every UI is:

1. Flat (no way to know what's clickable and what isn't)
2. simple, flat colors
3. has tons of whitespace

We'd be better off with separate UIs for touch and desktop