One side effect of cutting back my playtime is that the little administrative things that aren't as fun, like updating and maintaining add-ons, fall by the wayside. The other boring task that I avoid best I can is keeping my inventory organized, but this is easily solved by vendoring stuff. So when the version 6 patch dropped an ally my add-ons were hopelessly broken, instead of just eeking along through minor patches, I took the opportunity to delete my add-ons folder and take a look at the default UI which I had not looked at in literally years; it's come a long way.
My first revelation came shortly after starting a new hunter, since the best way to start anew is to start with a new character without any preconceptions or bias as to where things should be. I started questing with the default map and quest log and it was a better, more immersive, experience than with Carbonite, that bloated add-on that had replaced half of my UI for the better part of four years. I do miss the Googlesque map that I could zoom in and out and click and drag, but the default map is easy to navigate and my character actually pulls out a map when I am looking at it. I have also been playing SWtoR a bit in the lull before the expansion and was pleased to notice that the map window fades while walking so it is possible to see where you are going while referencing the map.
Next I did a little experimentation with moving the unit frames around, trying to get all the information I needed in combat more centrally located. At this point I was back on my main, a feral/guardian druid. I tried moving my unit frames to the bottom center, eventually gave up and it was time to bring in the add-ons. In combat I like to be aware of my health, whatever resources I need to use my abilities and a few static buff/debuff icons so that I don't have to search through rows of icons all over. I installed IceHUD, which I had used in the past for a death knight since the rune display was very helpful; that got me my health and resource bars, as well as combo points for my druid which previously required another add-on. Then I installed TellMeWhen since my add-on of choice, Auracle, hadn't been updated. After watching a YouTube video on how to set it up I muddle through the UI and had everything I needed to start raiding, except raid frames.
Raid frames were my second revelation; I have been using Pitbull since I learned what an add-on was. I had not seen the default unit frames, no less the default raid frames, for more than a few seconds updating add-ons after a patch. I went through the raid frame configuration tab and was impressed by all sorts of things when I started raiding with them. They show a nice glow for shields/absorbs, they show you who is getting rezzed, when someone sets up main tanks they show up in their own little group. Best of all, I didn't have to spend hours fretting over lining everything up perfectly and not overlapping anything.
It is still a work in progress, but I have updated the Add-Ons I Use page to where I am currently at, and will continue to update that as I finalize my add-on collection once again. Right now I am running with a mere 9 add-ons, which hasn't been true for at least 5 years; it is nice to see more of the UI as Blizzard intended.
The biggest shortcoming of the default UI is the lack of a customizable centralized informational display catered to a specific class/role/spec. I don't want to look at half a dozen places on the edges of the screen to figure out which ability to use next, I want to keep focused on whatever I am chewing on in the center of the screen and leave spatial awareness up to my peripheral vision. They already sort of started on this path by adding some basic power aura type graphics for procs, now they just need something like IceHUD and NeedToKnow.