The rules for seeing or not seein someone only become complicated when refering to Spot checks and even then those aren't that difficult to deal with or that common an occourance. They only take place on or before the first turn or in the event of a special ability that allows a unit to move without having to reveal it's card.
As far as differences, CC is no longer simultanious. No more instances of a BioGiant gettin to fight back against entire squads of people (and usually winning, the hundred hand slap was devastating). CC is handled like RC, except in a more personal way. CC stat +/- weapon modifier +/- any weird skills or conditional modifiers (IE charge or CC training).
RC targeting is the same as always, closest model in LOS of the closest unit unless a SA (Tac Sense or Sniper) overides it.
The rules are more or less a refinement of the second edition with a return of the first edition AR styles and the addition of cool effects like Smoke and more streamlined SA's.
as for realism, you do realise you're shooting space zombies don't ya?
Astro-demons aside, in terms of reality, morale has been expanded to panic and broken status (making it vitaly important to keep high LD Officers and Individuals around), there are still no uber god-on-the-battlefield units, and vehicles are nasty but not too big a problem for the wise player.
any specific questions?
-PFC joe