I've been playing FPS's for years; Doom2, Duke3d, HL1 (TFC+CS), Quake2+3, BF1942 to name a few, and can definitely say RO:O is one of if not THE best FPS I've ever played. If you want a change and are prepared for a bit of a learning curve for a couple weeks then give RO a try, once you start getting good at it other FPS's out now will look shallow in comparison. Heres some of the things I like about it:
Nicely balanced weapons based on rate of fire and accuracy, and the easiest guns to use well are limited in numbers per team. Often at least half your team will be using a bolt action rifle - one shot kill and very accurate but it takes time to chamber a new round, but you can get down behind cover to do that (manual rebolting). The bolt is like the rail gun in quake but is affected by bullet physics (it takes time to reach a target so you have to shoot in front of people and it dips very slightly) and you have a slow rate of fire and can not move about fast while in iron sights. The map often determines the type of gameplay - theres a very nice range of gameplay you can get, from mostly close range fighting with smg's/semi's to long range bolting with 100's of metres between you and the enemy. Theres also tanks which is a nice change for a while, but I really prefer the infantry combat, but combined arms maps are still good as long as the emphasis is on infantry
Free aim. When you aren't in iron sights mode your gun will NOT shoot in the centre of the screen unless you angle it so that it is point there. The angle is always moving as you move your mouse from side to side - to hip shoot well you have to learn to judge where the gun is pointing. Since iron sights take some time to come up often your best bet is to hip shoot at close range, especially with a bolt action rifle, but you should try not to get too close with a bolt unless you are good at hipping or stabbing.
Focus is on aim rather than dodging left, right, jumping while spamming shots at a target. Learn to aim well and control recoil (or burst fire) because you can't dodge about and just spray people in this game. Luck when trying to kill someone is not as important as most other games. People say the movement is clunky, but I think that its like this for these reasons - so you don't just move about trying to avoid shots. I never really had a problem with the movement..its smoother than INS anyway. Part of playing well is knowing when to change stance, and that it takes time to do most things so you have to time your reloads (and do it in a safe place), know when to sprint and when not to (because you can't shoot when sprinting and takes time to get your gun up again and uses staminer which makes your gun sway sooner in iron sights), know when to go to iron sights, know when its safe to change to grenades etc.
You often get some good teamplay, especially if you use your mic. Just use your map to see where to go and see if your squad leader has told you where to attack or defend.
Don't expect to own everyone when you first start. Just think about the cap zones and try to help your team win (remember its not just about the frags but helping your team to capture or defend objectives). It should grow on you once you start getting some idea of how to play well.
Oh and save yourself some time by watching these training videos, read the manual (download off the website) and do a bit of research on the RO forums if you want:
They don't mention tank angling which is a big oversight..angling makes your armour much thicker - just point the turret near 1 or 11..depends on the tank but thats basically all there is to it.