Those are huge issues for me in tablet mode. The charms bar mainly because it was a very quick and intuitive way to adjust brightness and volume. From my last use of Win10 a couple of months ago adjusting brightness was insanely hard, there was no toggle/slider and you had to dig into the brightness settings. Flicking through open apps and the desktop was also incredibly intuitive, it's actually such a nice feature I wish it was on phones as well. Full screen, well that speaks for itself, why would I want to go back to a desktop environment when I'm in an app? I think if they made the full screen toggle stick I would be fine with it, but as soon as you switch apps and switch back it's back to maximized view.
I just think MS is unable to think to both sides of the coin for some odd reason. 8.0/8.1 catered to tablet users, and they did a superb job of that. While I'm one of the few who sees virtually no issue with the desktop on 8.1 I guess many consumers did. Microsoft want MUCH too far with appeasing desktop users with features they didn't even want IMO.
Anyway this is all said with the caveat that it's a tech preview and we don't know what else MS will add back in. But with a "summer" release I can't see them really adding much in. I'm a huge MS fanboy, but I'm pretty sure I will stay on 8.1 on my touch tablets, what's sad about that is Win10 is free but I still probably won't upgrade to it.
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The icons are horrid, hopefully they are not final. I'm not necessarily a fan of skeuomorphism but I like nice detailed icons, not those cartoonish icons MS has.