Spawns:
Especially noticeable on the new version of Firing Range which is still one of the best maps in the game. Too often, I'll find myself killed at some point simply to be killed within 1 or 2 seconds 2-3 times before I am able to spawn and orient myself to any direction. Spawning is a players ticket back into the game and when he/she is systematically killed via spawning within somebody's direct line of sight, the fun fades fast.
This is true, spawning or the revenge spawn system doesn't work well to help a player who recently died, spawns him in almost the same spot where the enemy is.
Maps:
So many maps are simply so linear now. Modern Warfare 3 had the issue of overcomplication. We need to find a good medium.
I have no real complaints on the maps, they all have that typical COD feel to them.
a player can pop out and snipe me without receiving any damage
This is lag compensation program working, its how the game can balance various connection speeds. Part of online gaming.
Weapon Variety:
While weapons in this game are plentiful, they lack familiarity. The single AR-15 series M27 in this game is inadequate. For future titles, let's keep a minimum of two AR-15 series rifles and at least 2 AK models.
Not sure what you mean by familiarity, but I use the M27 and know how it behaves vs other AR's.