Lets Breakdown the new Rageblade

This is the new Rageblade

http://leagueoflegends.wikia.com/wiki/Guinsoo's_Rageblade

+30 attack damage +40 ability power Passive UNIQUE: Ranged basic attacks (on-attack) grant 1 stack, melee attacks grant 2 stacks. Grants GUINSOO'S RAGE at 8 stacks. Stacks grant +8% attack speed, +3 attack damage and +4 ability power for 5 seconds, stacking up to 8 times, granting a total of +64% attack speed, +24 attack damage and +32 ability power. UNIQUE – GUINSOO'S RAGE: Basic attacks deal +20 (+ 15% bonus AD) (+ 7.5% AP) bonus on-hit magic damage to the target and nearby units in an area of effect.

So, in essence, the base stats it gives would be equivalent to 870 gold in AP and 1050 gold in AD for an item that costs 2500. Or 1920 gold total without factoring in the passives. Each stack of the passive will give 392 gold in stats. So in order for the item to be cost effective you'll need to have 2 stacks of the passive active.

After the first auto attack, melee champions get a fully gold efficient item. Range champions with AA resets or Lucian can stack the Rageblade passive very quickly. The passive doesn't stack with on-hit effects like MF's Q. I have yet to try it on Ezreal, but I'm sure it will work the same way. The passive clearly states 'on attack' which signifies to me that it doesn't work with on-hit abilities unless it's an AA modifier like a Jax W or Nasus Q.

I want you to look at it with full stacks. At full stacks it gives you 64% attack speed, 54 AD, and 72 AP. With just the base stats and the first passive, at 8 stacks the item will give you 5056 gold in stats. That's a metric shit ton of stacks for an item that only costs 2500 gold. If you see someone with Rageblade farming a lane, stay away. An ADC like Lucian can get the most out of this because Rageblade stacks with his double AA passive. At will, he can stack his Rageblade to 6 stacks nearly instantly.

Guinsoo's Rage passive also works for ranged champions. For 20 base on-hit magic damage is worth about 400 gold. For every 13-14 AP you get the value of the on-hit is increased by 20 gold. For every 7 bonus AD you get the value of the on-hit is increased by 20. The Rageblade base stats along increase the value by 270 gold. So the passive increases the value by at least 670 gold. This brings the total to 5726 gold for a fully stacked rageblade.

On top of that, Guinsoo's Rage also creates a Tiamat effect on-hit regardless of being ranged or melee. I don't know how to calculate how much this effect increases the value of the item, but it's gotta be worth something. It's a bit of a double edged sword. It makes it easier to clear waves, but it also prevents you from sitting in a wave to keep your blade passive fully stacked allowing opportunities for the enemy to attack you without a stacked blade.

TLDR: Rageblade is OP and gives a metric shit ton of stats.