Notes/Deconstructions: Yes, he is a ninja, so no, he doesn't break the "only ninjas can use energy" rule.
Passive allows hard recovery denial in lane, can really hurt potion users much more than others. However does not reduce mana regen at all, that would be cheap. Note: Does not affect burst heals, e.g. Taric's Q, Soraka's W, Sona's W; nor mana/energy regen. Note 2: If you have 4 stacks, that means you regenerate Lifesteal/Spellvamp over 2 seconds, instead of instantly, if you have 10 stacks, it's over 5 seconds; if you have stacks, you will instantly recover any HP that you have left to recover when all the stacks go away-- e.g. if you have 30% lifesteal, and attack with 10 stacks on you, you will recover 3% of the damage you dealt each second-- but once all the stacks are gone (5 seconds) you will instantly recover anything left (15%)
W active benefits from both Life Steal and Spell Vamp in full-- basically (Lifesteal % + Spell Vamp %) * (20-140 + 150% AD) = amount healed.
All of his skills have two uses in some fashion-- Q is two different abilities (they share cooldowns, though), an AoE effect (basically a conical version of Thresh's Flay) or a leap. The rake can be used to harass, or in longer engagements be used after the leap for some sustained damage (though honestly, he's more assasain-esque; but he can stay in combat if he can keep damaging the enemy). This is even more important with Q2's passive, and Spell Vamp-- he will actually heal health from plastering the enemy tank with the skills he uses, as the tank will probably have Warmog's... and this will work in Shinoi's favor as eventually that 1.5% of Health per second becomes /damage/ against them (and he heals from the damage he's caused with Q2/Spell Vamp). E can be used to become able to not die while recovering energy, then hit enemies for damage.
In the end, Shinoi is a utility-based Assassin, featuring CC. He can 'Execute' enemies, though not as effectively as anybody with an actual Execute ability. He has a plethora of Damage over Time in his kit, and features around an anti-potion meta somewhat. (basically, if your enemy wants potions... they can't get them, I mean, look at that passive-- they'll definitely be loosing at least