- Sheen now grants 10% CDR instead of AP. Same goes for all of its upgrades. There is no CDR component, it just has CDR.
- Zeal has 15% AS and 20% crit. Seems to build into Hurricane and Rapid Firecannon, at the very least.
- Hunter's Talisman has +150% mana regen while in jungle, and its Jungler passive grants steals flat amount of health over time and grants bonus experience from jungle monsters (solution to lvl 2 rush?). It seems to have replaced Machete as the default starter (item code). Hunter's Machete scales with AS again.
- It seems like Trinkets change when you upgrade them. Upgrades currently available (Oracle, Farsight Orb) have their benefits and drawbacks listed. Oracles for example does not have a cast range (it works around your champion).
- New "greedy" starter items: Cull for powerfarming (grants some AD and flat life on hit, pays its full cost back after 100 cs, no more gold after that), - Seal for cheese midlane (basically mini-Mejais that stakcs AP on kills and loses on deaths).
- Dagger cost is down to 300, has 12% AS. B. F. Sword cost down to 1300, grants 40 AD.
- Tiamat is Pickaxe + one reju bead, costs WAY less
- BotRK remains as it was, costs 200g more. Changes to other AD items are already covered by most other comments here: Youmuu loses crit, Hurricane gains it, Malmortius is the new better Rageblade.
- New AS component that builds out of one dagger and upgrades into charge-stacking items (Shiv and Firecannon)
- Black Cleaver changed. Now has 55 AD, but only 300 health. Retains the passives, so it's Phage + something, and that thing isn't Kindlegem, unless - we're seeing errors and the components grant 100 more health than their upgrade.
- The Brutalizer is gone. Or rather, split into two items: Serrated Dirk (10 arpen) and Caulfield's Warhammer (10% CDR). I imagine that Youmuu builds out of two of them combined.
- Warhammer seems to build into some new items, like Death's Dance (spellvamp on physical damage and 20% damage is delayed as bleed, yeah Riven mains just came). And I guess it's the missing piece to Black Cleaver.
- New item that seems to build into Sterak's Gage, although it could end up upgrading into Frozen Mallet as well. Basically a Seeker's Armguard with same recipe as Phage and stacking HP (from 150 to 300 after 30 creeps)
- Essence Reaver: +65 AD, +20% crit, +10% CDR. Restores mana on critical strikes, grants bonus CDR based on crit from other sources. Core item on caster ADCs, like they said.
- Last Whisper has two upgrades: one with damage % bonus on fighting high-health targets, the other one combined with Grievous Wounds. Both grant bonus armor penetration, not total armor penetration. This is huge and I like it. Justifies the nerfs to armor items, as the tanks' base armor will not be shredded by LW and its upgrades anymore.
- Wit's End still sucks. Basically no changes, move along.
- Frostfang has +100% mana regen. Relic Shield has passive GP10. Talisman line lost flat MS.
- Twin Shadows are the new active on FQC. Nice decision, fixes both items at once.
- FotM active doesn't deal damage and slows enemies instead.
- Some minor component changes - reju bead is 150g, faerie charm is 125g, crystalline brace is 650g, sapphire crystal is 350g, etc.
- Captain enchantment is down to 450g! :)
- Boots of Swiftness seem to be 800g like Mobis. +5 MS
- Many armor items - including FH, Chain Vest, Zhonya's - are slightly nerfed. Price increases, sometimes with armor increase but not always.
- Many AP items had their price go up a bit. All previously 3000g items are now 3200g. RoA is 3000g, Archangel is 3100.
- Banshee's Veil and Spirit Visage grant 500 HP and 70 MR.
- Surprisingly enough, Ohmwrecker is unchanged. I guess they gave up.

Source

Defensive:

• Bond of Stone: +4% Damage Reduction. While near an ally this bonus is doubled and 8% of the damage they would take from champions is dealt to you instead (cannot reduce you below 15% Health)

• Grasp of the Undying: Every 4 seconds in combat your next attack against an enemy champion steals life equal to 3% of your max Health (halved for ranged champions).

• Strength of the Ages: Siege minions and large monsters that you or nearby allies kill grant you 20 and 10 permanent Health respectively (300 max). After reaching the max bonus further nearby Siege minion kills restore 100 Health.

Utility:

• Windspeaker's Blessing: Your heals and shields are 10% stronger. Additionally, your shields and heals increase your target's resistances by 15% for 3 seconds when used on an ally other than yourself.

• Thunderlord's Decree: Your 3rd attack or spell on an enemy champion shocks the area around them, dealing 10 damage per level plus 20% of your Bonus Attack Damage and 10% of your Ability Power as Magic damage to enemies in the area (30 second cooldown).

• Stormraider's Surge: Dealing 30% of a champion's max Health within 2 seconds grants you 35% Movement Speed for 3 seconds (10 second cooldown)

Offensive:

• Deathfire Touch: Your damaging abilities cause enemy champions to take 6 + 50% of your Bonus Attack Damage and 20% of your Ability Power in Magic damage over 3 seconds (Area of effect and damage over time abilities apply half of this damage over 1.5 seconds instead).

• Warlord's Bloodlust: Critical strikes heal for 15% of the damage dealt and grant you 20% attack speed for 4 seconds (2 second cooldown).

• Fervor of Battle: Your basic attacks and spells grant you a stack of Fervor for 5 seconds (max 10 stacks). Each stack of Fervor adds 1-8 bonus physical damage to your basic attacks against champions, based on your level.

Defensive:

• Recovery: +0.4/0.8/1.2/1.6/2.0 Health Regen per 5 seconds

• Unyielding: +1.2%/2.4%/3.6%/4.8%/6% Bonus Armor and Magic Resist

• Tough Skin: You take 2 less damage from Champion and Monster basic attacks.

• Explorer: +12 Movement Speed in Brush and River

• Runic Armor: +1.6%/3.2%/4.8%/6.4%/8% bonus to all shields and healing on you (includes lifesteal and regeneration).

• Veteran's Scars: +1.2%/2.4%/3.6%/4.8%/6% Bonus Health

• Insight: Your summoner spells have 15% reduced cooldown.

• Perseverance: +50% Health Regen, increased to +200% when below 20% Health

• Swiftness: +3%/6%/9%/12%/15% Tenacity and Slow Resist

• Legendary Guardian: +0.4/0.8/1.2/1.6/2.0 Armor and Magic Resist for each nearby enemy champion

Utility:

• Wanderer: +0.6%/1.2%/1.8%/2.4%/3% Movement Speed out of Combat

• Savagery: Basic attacks and single target spells deal 1/2/3/4/5 bonus damage to minions and monsters

• Runic Affinity: Buffs granted by jungle monsters last 15% longer, including Epic Monsters and River Shrine.

• Secret Stash: Your potions, flasks, and elixirs last 10% longer. Additionally, your potions are replaced with biscuits that restore 20 Health and 10 Mana instantly upon consumption.

• Merciless: Deal 1/2/3/4/5% increased damage to champions below 40% health

• Meditation: Once every 5 seconds, regenerate 0.3%/0.6%/0.9%/1.2%/1.5% of your missing Mana.

• Bandit: Gain 1 gold for each nearby minions killed by allied champions. Gain an additional 3 gold (or 10 if you're melee) when hitting an enemy champion with a basic attack (Cannot occur more than once every 5 seconds).

• Dangerous Game: Champion kills and assists restore 5% of your missing Health and Mana.

• Precision: Gain 0.6/1.2/1.8/2.4/3 + 0.06/.12/.18/.24/.3 per level Armor and Magic Penetration.

• Intelligence: Your Cooldown Reduction cap is increased by 5%, gain 5% Cooldown Reduction.

Offensive:

• Fury: +0.8/1.6/2.4/3.2/4% Attack Speed

• game_mastery_displayname_6112: +0.4/0.8/1.2/1.6/2.0% increased Ability and Spell damage

• Double Edged Sword: Melee- Deal an additional 3% damage, take an additional 1.5% damage. Ranged- Deal and take an additional 2% damage.

• Feast: Killing a unit restores 20 Health (20 second cooldown)

• Vampirism: +0.5/1.0/1.5/2.0/2.5% Lifesteal and Spell Vamp

• Natural Talent: +2/4/6/8/10 Attack Damage and +3/6/9/12/15 Ability Power and Level 18

• Bounty Hunter: You deal 1% increased damage for each unique enemy champion you kill.

• Oppressor: You deal 2.5% increased damage to targets with impaired movement (slow, stun, snare, taunt, etc.)

• Battering Blows: +1.4/2.8/4.2/5.6/7% Armor Penetration

• Piercing Thoughts: +1.4/2.8/4.2/5.6/7% Magic Penetration