I played a few games with the new update, and here are my thoughts .
I personally don't like them. The conversion from health to resists specifically, but also the reduced sunfire damage and lack of options when behind.
At first I thought it was going to be great, that tanks would spike less, but then I realized, if a tank ever gets behind ( which is quite often ) they are at a MASSIVE disadvantage because they can only afford to itemize against one type of damage. Experiencing it firsthand, I never felt tanky at any point in the game, and the resistances I had meant less as people got more armour pen.
Secondly, as a sion payer and a lover of many champions who used sunfire, basically every champion was balanced around its damage both to minions and champions. Since the item basically just got straight nerfed, so did every tank in the game. Champions like poppy who were totally balanced around sunfire's damage to champions are now much weaker than they should be.
Champions who don't rely on sunfire for waveclear don't have any good options for mana sustain in lane either. IBG is ok, but only gives armour which is problematic when dealing with any damage but physical without % pen. Similarly, FH only gives armour and is bad vs anything but ad. RG has decent stats, but it's active is so bad in general that it's not worth buying at all.
Additionally , the lack of health just feels wrong. It's incredibly unclear who is and isn't tanky now. Health shows a very visible difference when you have lots vs little, but resists don't. This is a MASSIVE gameplay clarity issue, and often results in poor feeling and understanding.
Finally, any source of true damage and armour shred in kits just got disproportionately better, and riot has done nothing about that. I expect them to do something eventually, but eventually isn't very soon is it? So as of right now anyone with built in true damage or armour shred of any kind just sucks to play against.
Also red buff.
Red buff is too good.
So, after my first five games these are my concerns, gripes, and grievances with the new system. Hopefully everything ends up in a decent spot soon, because if nothing changes I might just stop playing altogether. That might be an overstatement, but so far, the game I used to love isn't there anymore.
Anyway, that would be just about everything I have.