Since some of you seem to be having problems with the pace / speed / mechanics of the game, figured I'd post some helpful links / tips for those of you who are either new or haven't played the BF series competitively.
Firstly, symthic's weapon stats:
http://symthic.com/bf4-stats
Utilizing the above stats, a few weapons to shoot for, early to mid unlock range include:
Assault: M416; this is my most used weapon.
Carbines: ACW or SG553
PDWs: Lol.
Recon: M40, but it's really just a matter of understanding bullet drop relative to the scope and weapon you're using (e.g. bullet velocity and bullet drop in m/s^2)
Support: U100; incredibly accurate weapon.
Rockets: RPG, all day. You also get to like what you see in the mirror but not using the atrociously broken LAW.
Tanks: HE Shells, HMG. That is all. Rear shots are fucking hilarious, and IFVs are cannon fodder from any angle. Two shots max if you know what you're doing, even from the front.
As far as attachments, I've generally been putting a muzzle brake on everything outside of long range weapons, but this doesn't prevent me from being able to snipe kids from 150m out with the support weapon above.
If you're engaging in a lot of close quarters strafing action, take the vertical or ergo grip, whereas if you're focusing more on versatility across all ranges, go for the angled grip, as this will create tighter ADS bursts across all ranges. I use the latter predominately with the 416, along with the muzzle brake.
Sights are a bit of a toss up and mostly a matter of personal preference; RDS and Kobra are both legit, but in certain spots (e.g. the snow flanks on Operation Fuckfest Locker) the RDS dot becomes transparent, which is why sights like the HD-33 (U100 default) are quite nice. I'm trying to get this for each weapon, but unfortunately it's battlepack only (fuck off, DICE).
Random notes:
Fuck bipods, the sway with large mag weapons like the T88 and so forth is absolutely atrocious, unless you use a compensator. Even then it's still nothing like BF3's. This is a good thing, imo.
The M320 flashbangs are fucking hilarious on maps like Operation Locker.
The SRR-61 has incredibly low bullet drop, which combined with its bullet velocity makes for the flattest trajectory of any long rifle I've seen in the BF series. The M98B may have slightly higher velocity (650 to 620 m/s) but it has over 50% more bullet drop (9.81 to 6 m/s^2), which means less adjustments for incredibly long range shots. One full mill dot on a 6x scope was taking my shots out several hundred meters.
The REX is shitty compared to how quickly you could perform follow up shots with it in previous games; I still use it for quick "oh shit" moments nonetheless, and so that I have more bang for my buck when I'm down to nothing but a sidearm. About to unlock the shorty 12G, will let you know how that works out.
As far as general gameplay is concerned, think about it as a game of principles which are absolutes that cannot be broken. The infantry combat isn't nearly as fluid and aggressive as it was in BF3; you must be careful and thinking about both the macro and micro situation as it pertains to you at all times to keep yourself out of the large amount of exposed areas which become killing grounds filled with the less experienced players. If you see a route that has more cover, but might take you twice as long to get to your destination, take it.
Some of you have been on our mumble server; I'll see if I can't set up a visitor-only channel outside of my Lesbian love shack so that I might be able to give some of you random guys tips as you need them.