22% criti Chance combined with 10% Criti Damage. Lethality (Criti Damage) is completely useless, unless its purpose is for Heartseeker. But your target has to almost be dead to augment the extra criti damage.

Lets just say you criti at 25%. Lets say your normal damage is 200, making a criti worth 400.

4 hits = ~1 Critical Hit.
200 + 200 + 200 + 400 = 1000 Damage in 4 attacks
+10% Critical Damage will only increase that 400 to 440 dmg, for a grand total of 1040.

instead Shift those 3 points into 1 point of Defensive mastery and 1 point into the 15% Mpen, and 1 point into Ignite Mastery. Skills are based on Magic Damage to you will increase your total damage.

Build is alright but I always start with spear shot first. Low CD so you can use it multiple times at first gank and does nice damage. I usually start with a Long Sword first then get berserker greaves, then turn the Long Sword into the Occult (depending how the game is going. If your not doing so hot then just turn it into a Black Cleaver or Last Whisper late). And I also recommend getting the Infinity Edge first for it's passive, seeing your heartseaker's passive is automatic crit if their health is < or = to 15%. And also going 21/9/0 i think is better putting the points in dodge and in Nimbleness instead of 4 more magic resist and .75% less CD.

Good, but last whisper's passive doesn't stack with black cleaver's passive, so it's sort of useless.