The full set of changes can be found on Surrender@20's set of PBE changes but essentially:
• Q, auto attacks, and ult proc his W's passive. Q does so by applying it to all units you pass through.
• W passive no longer has a missing health component, and the active got changed to a single on-next hit effect instead of an auto-attack modifier for 6 seconds. If W's passive was on your target for at least 2 seconds when you use the active, the damage is tripled.
• W essentially resets on target kill and refunds half the mana.
• Aforementioned ult changes.
Basically, lower sustained damage for arguably stronger burst that you have to time correctly.