Vesting periods on employee stock options
You get ten free games a year but other than that it's pretty average benefits/perks; although I think as talent becomes harder to attract then this could change.
The employee share participation program is basically 15 percent minimum guaranteed free money regardless of share price fluctuations if you use it effectively.
best thing is the stocks. Worst thing is sitting through an hour long lecture just to understand how to pay the tax on those stocks.
List based on reports from current and former employees. It may not be complete.