My other favorite game besides NS2. Requires just as much team work as NS2. Turns Battlefield and CoD into a joke when you play a game where this kind of team work is crucial.
Usually when there's a seasonal sale it will go on sale for like $5 or $10. Just buy Rising Storm (a later released mod) when it's on sale since it will come with RO2. Steep learning curve but NS2 had one too and is fun. 
Don't bother with Action, just play Realism. That's really what the game is about. RO never tried to be a CoD but since that's basically the FPS genre of today they kind of had to include Action. Rising Storm is a more action orientated and may be easier to get into than RO2. It's brutally difficult (half the time you die you'll never even know where the shot came from), RO2 in particular, but making a kill is just that much more rewarding.
Pro-tip, don't take Commander role until well experienced just like in NS2. 
Right about to hit 80 honor and it's going to give me about 5 class upgrades at once. Been a long time coming.
If you want a very brief summary watch 6:05-7:05.
