Some of the item icon changes are better, some are worse, some I'm indifferent to. It's a mixed bag.
Armlet is worse I think - less distinctive.
Blink dagger put on some weight - looks pretty bad now.
Poor Man's Shield no longer seems to be fitting of its name.
Vanguard, I think is harder to decipher that it's a shield rather than a mask or something - change for the worse.
Skadi change is okay, though the all-white background was distinctive.
The skinnier/zoomed out Quarterstaff kind of bugs me, but I'm fairly indifferent to that one.
Orb of Venom is subtle, but I think a change for the worse.
Medallion of Courage is an overall improvement I think. More detailed.
I like the new Magic Wand.
Hood I'm fairly indifferent to. Probably an improvement.
Heart is slightly worse.
Headdress I like the new one, but I think the old was pretty distinctive as well.
Couriers are awful now.
Dagon is improved.
Chainmail is more detailed - better, even though it's actually scale mail in the icon.
Bottle is worse.
Kinda like the glowing eyes on BKB.
AC is changed, but not necessarily better or worse - just different.
Drum - eh?
Wards are most definitely worse. That orientation just doesn't look as good.
Side-by-side comparisons that I'm referring to. Other ones I didn't mention may be very subtly changed, but are pretty much the same.