Sure there is "under the hood" stuff. As for the more obvious stuff...
1. Due to the start panel I haven't enabled the Desktop Toolbar that I use in 8.1
2. Due to the start panel I haven't created the Applications folder/window that I use in 8.1
1 & 2 I do in 8.1 so I can access everything w/out changing screens.
However, I am, really, not sure that I maybe prefer the way I have things in 8.1. It is clean & simplistic. The start panel I find big, cumbersome & too 'involved' or complex, too much 'looking' for things. True it can be 'sized' but, not as I, personally, would like; can't make it narrower... taller or flat & wider but, not narrower when left on the vertical. Nor do I need all those tiles on it (or any) when those wanted can, already & still, be pinned to the taskbar... I don't bother w/ Start screen or its tiles in 8.1 so, don't, really, care about having them in my face in Win 10.
The one thing I have always wanted was to not have APPs opening Full Screen & covering Desktop... til I made things share the real estate. Ergo, the one thing I, really, do like is that APPs can, now, be movable, sizable, 'windows' on the Desktop. What I do not like is they, STILL, open Full Screen initially by default, until I do something. That stinks and should be the reverse by default... let me have to do something to make them Full Screen, if I want (that).
I am running mine as a VM. Where it is a possibility Win 10 may be ultimately, eventually, pushed out as a Windows Update OR an Upgrade from the Store, as was 8.1, nothing prior to a GA, a final release can be considered an update. Nobody should be replacing their 8.1 w/ these previews. They are the equivalent of Betas. On a spare box, dual-boot or VMs but, sure not treated as replacements. After going through Beta Testing Vista, Win 7 and Win 8 for & with Microsoft, you do not put pre GA Builds on production machines. PREview as in PREfinal. Hell MS even tells people, you do this your original recover partition is gone, there's no turning back... and that's fine if a GA but, damn risky & foolish w/ betas.
Any, I may or may not, Keep using the start panel; heck, I had quit using anything like that in Vista or 7 long before I had even heard of 8. But, if they change it, as I (except I'm only 1 person) requested so APPs don't open, initially, Full Screen, I could be ok w/ Windows 10... especially, if the price is right. But, that said, I sure do like 8.1 especially, the way I have it designed
( read, set up or configured).
The thing is people tend to focus on the cosmetics, the blatantly visible, the mechanics. Sometimes we lose sight of or miss the huge engineering & technical strides in Win 10 or from the 7/8 era to 10. I won't go into it here... there are lots better places & articles explaining the concepts well. Suffice to say they are exciting, drastic and very impactful. 8 was, as we thought, only a wee hint or beginning of what computing is becoming. Oft when we look @ the picture on our (individual) monitor, we are seeing the big picture. Things are being designed & built for Enterprise, for a whole globe full of End Users and for an evolving, changing digital landscape, society, culture and future. Usage, wants, demands and we people take or will come to take for granted and consider to be the norm is going to have a very different complexion very soon.
I always remember, as I watch things morphing, at a Microsoft conference a very few years ago as the presenter stood on stage w/ a wee cell phone in his hand and said soon it will ALL be right here in your hand. And a few hundred people laughed & scoffed thinking he was being very Orwellian. Yet, already, now, we have Cloud and BYOD and a growing Mobile work force, security concerns, hackers, identity theft, encryption and Bit-locker, young kids with Smart-phones and elementary schools requiring pupils to have laptops.
It is not, any longer, a matter of whether we want or need a new OS or not or looking to justify migrating or holding back. It is, now, more a matter of accepting the reality of OUR world... we asked for, we created it and the pace is rapid... quicker than many realise and not all can or want to stay in step. After observing the massive, speedy differences over 60 years, I'll end with this... 1984 was published in 1949. By the time 1984 had arrived, @ least, 90% of what Orwell fantasied in the novel, actually, existed and was in daily, widespread, use.
Cheers,
Drew