You lose a couple of minor things that you probably were using alternatives for anyway for the most part. You lose native DVD player because Media Player is now gone. You'll also be forced to do auto updates if you have a Home Premium version or below. Supposedly, there may be a package manager with it where you can just type in what you want for a program and it finds it, installs it and maybe keeps it updated for you automatically. MS touts this as some genius idea that struck the design team once again leaving Linux out of the credits who have been doing this for around 12 years now. They did the same with Volume Shadowing and Transparency and so-on in the past, so I guess nothing new.
It seems like it will be decent though but I do have a problem with their UEFI implementation for OEMs (it wouldn't affect current PCs though). They are going to force Secure Boot to be on and remove the 3rd party certificate authorities. It may not seem important to anyone but this means they are attempting to force Windows as the only OS that can be installed onto the PC.
I'd imagine there will be outrage from the open source community just like when MS tried to do something similar with Windows 8. Secure Boot was on by default but you could turn it off. After the outcry, MS offered a CA for the Linux Foundation who made a bootloader for all Linux distributions that will work with Secure Boot enabled still.
I also don't think Secure Boot brings anything extra to the table. It is there to keep malicious software from writing itself pre OS boot (ie. the boot sector). You probably haven't heard of anyone ever getting a virus like this because nobody bothers anymore. Back in the 90s when this could happen, BIOS developers made their own protection where they had a rudimentary virus scanner scan the boot sector and even give the ability to lock it out. But MS spearheaded the "UEFI standard" to which they own the certificate key database to (so much for an open standard). There touted feature was that UEFI forces developers to make a GUI where a mouse can be used, basically so it would look pretty instead of the normal blue background screen with white lettering that you navigate with the keyboard, which was already around, just not something many OEMs bothered implementing. The exception that I can remember is Dell but that's it.
Anyway, take it all with a grain of salt. You can go ahead and reserve it now and not install it until you get the reviews in and wait it out if you'd like.