I have no idea why Redhat made so many changes in their most recent release, but it is so vast that it may as well be a completely new distro. To name a FEW:
Anaconda RHEL installer completely redesigned
Legacy GRUB boot loader replaced by GRUB2
Adds a bit of complexity to it, but GRUB2 is much more versatile than old-fashioned GRUB. Besides, it's also much more mature now.
Procedure for bypassing root password prompt at boot completely different
As long as [sudo] su - still works (with any kind of password), I'm happy. It's root. You're not supposed to bypass the password prompt! But, if you really, really, want to, you could always issue init=/bin/bash at the kernel command line in grub. Used to work with lilo, still works with grub as well.
SysV init system and all related tools replaced by systemd
The sheer horror. Seriously, another reason NOT to use Red Shit.
ext4 replaced by xfs as default filesystem type
That, at least, is an improvement. Both ext3 and ext4 have fundamental design flaws (like kjournald (and alike) that pops up every five seconds and slows down your system to a grinding halt if you're especially unlucky because it fails to check if it's already running). XFS is a much more robust design in any case, and way, way faster to boot!
Directories /bin, /sbin, /liband /lib64are now all under the /usrdirectory
Not too sure what to think of this. On the other hand, Solaris does basically the same and has been doing that for a quite while.
Network interfaces have a new naming scheme based on physical device location (e.g., eth0might become enp0s3)
Not sure what to think of this either. On the other hand, various UNIX variants do more or less the same.
ntpdreplaced by chronydas the default network time protocol daemon
Hmm. Not familiar with that one. Is that the one that will absolutely refuse to update your time and date completely?
GNOME2 replaced by GNOME3 as default desktop environment
Arf. Gnome. Nuff said.
System registration and subscription now handled exclusively with Red Hat Subscription Management (RHSM)
I blame Oracle for that.
MySQL replaced by Mariadb
I blame Oracle for that too.
tgtdreplaced by targetcli
What a shame. Last I checked, tgtd was just about the only ISCSI target daemon that made any kind of sense. But I admit, it's been a while.
High Availability Add-On: RGManager removed as resource-management option (in favor of Pacemaker)
Just a symptom. WIth systemd as the beating heart of your system, you'll need that Pacemaker. Especially if it's in the death throes of the log corruption you are bound to get.
ifconfigand routecommands are further deprecated in favor of ip
I love the 'ip' command. It's powerful. Still, for heaven's sake, let's keep the old commands?
netstatfurther deprecated in favor of ss
Stupid decision. Netstat is at the core of many a UNIX admin's skills.
System user UID range extended from 0-499 to 0-999
Couldn't care less. As long as I can reserve 1000 for myself (pun intended).
locateno longer available by default; (available as mlocatepackage)
Hmm. Why on earth would one want to do that?
nc(netcat) replaced by nmap-ncat
Well, nmap is a powerful tool. This, for once, makes sense to me.
Systemd is pain to use for me and feels backwards... I find troubleshooting processes with it to be more frustrating than anything else Redhat has done in the past 20 years... Well, almost.
More frustrating than using what's basically a GUI-only installer on a system that really does not need a GUI in the first place? Sure, you can use the anaconda text mode installer, but it does not support LVM and if there's one thing you really like on any Linux system, it's LVM. It's clean, it's mean and it's easy to setup and use. Actually it's easier to setup outside any installer, but anaconda (at least in text mode) refuses to pick it up and will happily propose (and if you let it, setup) a non-LVm installation for you anyway.