Can't wait to get a PS4 and squad up with you guys that have it. Conquest is the KIng of gamemodes for me, but you can get a serious hammering from an organised team. One full squad working together using all classes can rule a 12 v 12 match on the PS3, bu this may not be the case on the PS4.
I've played a lot of TDM and a fair bit of DOM to level weapons up, but need to give Obliteration more a go, what put me off was a timer being added to the matches, not sure if this is still the case, and I need to play more Rush as this game mode can be awesome if the battles are tight and don't end up in spawn trap killfest.
Most have already stated the obvious one's and tbh Gary, everything I told you for BF3 runs true for this game. Yes, it's a tough leaning curve, yes it can be seriously frustrating as a beginner (not going to call you a noob because I know you're pretty handy in CoD).
My favourite vehicles though have to be the armoured jeeps, with a decent driver and gunner those things can totally wreck a team.
Level guns up as quickly as possible to get the best set up's for you! Don't bother too much with LMG's for Support class they seem way weaker than in BF3 and the suppression system has changed to them even more. Carbines or shotties seem to be the way to go with this class now for me as I've pretty much given up with the LMG's.
AR's are still the best primaries imo, I particularly love the SAR21, slower fire rate, but offers more control (this is Hardcore though) higher fire rate weapons seem to give you more advantage in Normal mode.
I've yet to start using the DMR's or Shotties so can't comment on those, but the Carbines are good and once unlocked via the Engie class can be used for all classes.
Bolt action rifles are god like in HC, one hit kill anywhere on the body as long as you're not too far away or else you'll need a headshot. Ryan swears by the Shorty 12G as a secondary, but I've yet to use it as I'm trying to master the default pistol before moving on.
Impact nades are brilliant Nade launchers are great when running assault class, but means you have to give either defibs or med packs. C4/Claymore's for both Support and Recon was a good move imo.
I hope you learn to like this game as it can be very rewarding!