I've been sucked in again, since I have some friends to play with. It really is quite fun. The game rewards patience and working with your teammates instead of just chargign blindly ahead and getting exploded. the main gripe I had with the game - that free accounts couldn't start groups so at least one person had to pay for friends to play together - is being alleivated somewhat in the next patch, with 2-man groups being allowed for free accounts.
If you're going to start playing, I got a few tips to get you started.
1) If you ever intend to spend real money on anything in the game, go for the premium account. 50% extra credits - after repairs - almost doubles your income. The premium tanks are a trap. They may earn you decent credits, but you'll have to pay additional gold coins to transfer the XP they earn onto the regular tanks.
2) For tiers 4-7, Russian tanks roflstomp pretty much anyting in the game. On tier 8 and 9, everyone's sort-of even. If you just want to drive around and explode shit, go for the KV. That said, the german tank destroyer tree - especially the Marder II, the StuG III and the Ferdinand are extremely good for their tiers.
3) Tier 4 and 5 tanks generally earn the most credits per match after you pay for repairs and ammunition. Keep some around as moneymakers.
4) The inverted V in your targeting reticule will change colour when it's over a tank to show you the chance you have of scoring a penetrating hit. If it's green, you have a good chance (almost guaranteed except when sloping armour causes your shell to bounce). If it's yellow your chance of scoring a penetrating hit is around 50% and if it's red, you may as well switch to HE rounds or find another target.
5) If you're a small tank facing a big tank, and hiding or running in circled around it isn't an option, go for module damage. Shoot the tracks to immobilize it. Shoot the gun and rangefinder to keep it from shooting at you. A HE round on the gas tank or engine has a ~20% chance of causing a fire which can really ruin his day.
6)
Read this page. Especially the sections on ammunition and penetration. It covers a lot of things that aren't explained in the manual. Also note the section on earning experience. One of the highest-earning matches I ever had I was a Tier 3 tank in a battle with Tier 7's and 8's. I found a bush to hide in, spotted the enemy heavies for our artillery and raked in tons of credits and XP for lighting up the enemy without ever firing a shot.
7) Take some time and read up on the different tank trees before commiting to one. It'll generally cost you a lot less grinding for credits and XP to focus on one paticular line of tanks, since many submodules can be shared between them. If you try to level up tanks in several different trees at the same time, you're going to be stuck with tier 1-4 tanks for quite a while.