i got the game at launch on steam and later bought it off a dude on craigslist for the 360. i end up playing it more often on 360 just because the pace feels a little slower and it gives me a chance to learn the special infected (SI).  eventually i'll move on to PC when i learn the maps a little better and not holding back my team.
 
so far, im digging the new SI. here's my raw impression of them.
 

•  the charger is a beast especially if you're able to hit a couple of them in the process. the time it takes for the survivors to recover is pretty long. his melee does serious damage too. to balance that, they gave the charger a ridiculously long stumbling animation if he misses a dude.

• the spitter is a huge game-changer and totally compliments the SI crew. it's probably one of my favorites to use.  his long range acid attack is awesome. if you're fighting a dude with a melee weapon only, you can have him try to chase you. that small trail of spit that it leaves behind also does damage to the survivors. they'll learn real quick to not follow you.

•  i still need more time to learn the jockey. i noticed he has a lot more health and can jump a lot higher than the rest of the SI. one of the things i need to try out is see if i can ride a dude while i jump in mid-air. if so, that opens up a few possibilities. so far ive been using the jockey on same ground level as the survivors and just hiding behind stuff waiting to pounce one of them, but if i can jump on a dude from above? watch out!

• i rarely get the hunter now, but it seems like his leaps are a lot faster and is more difficult to shoot down mid-air due to the blur effect he's got going on now. he still deals a lot of damage and one of the times i got to play as him, i incap'ed a dude in no time.
  

• the smoker's range feels shorter... i dont know if they messed with that or not though. maybe im just not gauging the distance properly., plus i dont get to use him often either. oddly enough i incap'ed a dude with him too!
  

• boomer is still fun to use, but the same issue from the last game is still present; puke on a dude before or after a zombie wave and you wasted a bile shot- no zombie wave.

• the tank is still just as brutal, but with all the new tools available to the survivors, it does make taking him down a little easier and a lot less scary.