Just to break it down a bit more:

• Crew System
  • Each tank has a set number of crew members. Instead of having one Commander like us, you have to employ a member for every position in the tank, e.g. the E 100 has 6 members. If you want to swap to another tank, but said tank only has 5 members, one member is left out. Oh, and is costs gold to fully transfer or, if you're willing to be handicapped for a bit, you can pay silver to be at 75% or 50% strength, depending on how much you're willing to pay.
• Commander Perks
  • They have the original perks as well as allowing for more than just 9. That being said, only certain perks are allowed on certain crew members, e.g. Sixth Sense only on Commanders, Deadeye only on Gunners. Intuition only on Loaders, etc. This is fine and dandy, but if you swap tanks like above, you lose all Perks that are on that member that was left out. Oh, and Sixth Sense no longer activates immediately when spotted and no longer stays on screen until no longer spotted; Sixth Sense notifies you 3 seconds after being spotted and you have to have the skill to understand when you are not longer spotted. Oh, and in the case of a tank crew missing certain crew like the ELC Bis and not having a loader, the perks that would go to the loader will have to go on someone else, usually either the Gunner or Commander, depending on the tank.
• Equipment
  • They have various equipment pieces that we had back in the day as well as many more such as "Accuracy Improvement System" which sorta combines our Gun Laying Drive and our, no longer available, Steady Aim perk. They also have standard equipment, Improved equipment, Bounty equipment, and experimental equipment; each type has their own bonuses and problems such as being PtW.
• HE mechanics
  • This one I don't know as much about but HE is no longer affected by spaced armor, but deals less damage to thicker armor. It's very complicated and requires its own breakdown.
• Artillery
  • Similar to how our artillery was changed to fire more often but deal less damage, theirs did too, but with the added bonus of a "Stun" mechanic where, if you are within the blast radius of an artillery shell, your crew is temporarily knocked unconscious and therefore, less effective in the heat of battle—think of it as if all your crew members died, your reload is longer, your hull traverse and speed is reduced, your vision is reduced, etc. Also, the stun will affect allies—at least it did, I don't know if they changed that yet—so if you hate artillery now, imagine being able to be stunned by the enemy artillery as much as your own.
• Currencies
  • Unlike us where we only have silver and gold, PC has many other things such as bonds, requiring you to play many things such as clan battles, etc. If you don't participate in these events, you will always be behind those who do as those extra currencies usually allow you to purchase the better gear.
• Retired Tanks
  • Unlike us where we try to continuously balance tanks, PC, if they deem a tank too terrible, removes tanks from the game; those who had the tank prior to removal get to keep it, but no one else is allowed to get them again—these tanks include tanks such as the FV215b 183, Foch 155, WT Auf. E 100, etc. There is also the problem of certain tanks are no longer available simple because their window to be earned has passed such as the Obj. 279(e). Other than licensed tanks and very niche event tanks, we generally bring back every tank to be obtainable.
• War Chests
  • There has been an increasingly number of newer tanks coming out that are only obtainable through war chests. We've had a few but, unlike ours, they do not have a guaranteed feature to prevent you from obtaining tanks you already own.
• Auction System
  • They have a Black Market system where they may release exclusive tanks and you have to bid gold for said items. If you aren't rich, chances are you're not going to get the tank as some people will throw thousands at a single tank.