Thoughts so far...
-I like the new concentration system. It seems to be used in a lot of place to tone down mega buffing and to limit the potential of things like Dominate. It seems like it may keep classes in their role, rather than allowing spellcasters to outright replace fighters at higher levels, etc. so long as those sorts of buff spells continue to be placed under duration: concentration. Can still pre-buff a proper spell to concentrate on when scouting goes successfully.
-Not sure why a Wizard would not take 2 levels of Fighter. Action surge and armor proficiency seem to be a lot greater benefit than Ability Score Improvement and Signature Spell. Actions still win, presumably. ASF% is replaced with just whether you are proficient or not.
-Similarly, the Rogue is probably better off with 2 levels of Fighter, and even perhaps a level of Wizard for at will cantrips to ranged sneak attack with.
-Better attack options, rather than need for pounce to full round
-No need to feat up the attack options, so the Fighters extra attacks can often be used more tactically (grapple, bull rush, etc).
-Some IP proofing built into Fighter & Rogue, ok.
-Dead levels / boring class features. Simply not as entertaining as ToB, at least not from reading.
-Heh, Divine Intervention is quite an interesting longshot, 10-19% chance perhaps, holding on to for BBEG, or maybe for True Res.
-I think I like the ditched caster level for spell improvements based on slot used.
-I think there's some interesting setups in the Fighter/Rogue/Wizard multiclass space, but not so much in the Cleric space.
-On one hand, I appreciate a lot of the simplification as it will speed up higher levels of play, which in my experience gets bogged down at a physical table. However, I'll also miss that higher level of complexity when applied to pbp or just mmx theory in general.
-No stat prereq for max level of spell cast, or did I miss it? Gishes don't necessarily have to care about their casting stat?
-Short & Long rest does a bit to alleviate the 5 minute adventuring day. In the basic rules there doesn't seem to be an auto safe sleep, Rope Trick, etc. Though once you gank an item from a location, Teleport is reliable.
-Still need to see the full core books and what feats look like.