When I first played this game, I was very amateur to first person shooters. I caught on quickly and I was undefeatable because the AI became very perdictable, i also played the game so much on single player that i memorized every detail and location of computer players. I then started playing this game online. I was very surprised at this point because everyone who played was far superior then I, i even got to a point that i was about to quit playing because it was so difficult, id also like to add that it was so common to have a player that used a cheat, also known as a bot. a bot is a computer prgram that does the work for you. After awhile I caught on and became a server owner/clan leader and owned my own clan, and then we went on to become undefeated for almost 6 months!
I would highly recommend this game and its future installments just as long as you can play online, and deal with the headache of cheaters. If you can play online (and its free) then this game will become an addiction that will never leave you!