It seems like from watching all the interviews and developer diaries on this game that Treyarch has had an axe to grind with sniping since the first planning meeting of this game.  At launch the sniper classes were basically what you should choose if you wanted to have your ass handed to you in anything except Search and Destroy. We've been promised measures that will level the playing field but even after a title update that was supposed to "fix" the sniper rifles to make them more competitive, they're still impractical to use because of several issues.  
 
First, The sniper rifie, by design,  is best used at a distance and with the exception of 1 map (Array) that's IMO actually best suited for it, most of the maps are not.  Most of the maps have a  tight corridors or such a limited number of sniping positions, many of which that are easily flanked from multiple angles, that choosing a sniper class often becomes a recipe for failure
 
The other problem besides the map design is that the sniper rilfes in this game just don't handle as well.  The generous aim assist that was present in Modern Warfare 2 has been dialed back  in this game and as such, sniping requires more precision.  Conversely most of  assualt rifiles, LMG's and even SMG's in this game  handle better and are more than capable of taking out the same target at medium to long range.  As if making a sniper's primary weapon nearly useless by comparison wasn't enough, Treyarch also dialed down the damage dealt by the pistols in this game effectively leaving a cornered sniper without a close range weapon to fend off a rushing opponent, again leaving the deck stacked against a sniper.  
 
The final nail in the coffin for the snipers, which is one i don't really have a problem with "on paper", is the decision to take measures against quick scoping.  In case anyone doesn't know what that is, just go to youtube and type in quickscoping and see for yourself.  Now i'll be the first to admit the rage that consumed me when a quickscoper would decimate my entire team in MW2, but coupled with the rest of the changes listed above, this just comes off as overkill.  The snipers are effectively nearly useless class unless you need a last resort tool to take out a person who's been dug-in a particular location and all other efforts have failed. 
 
In short, i think Treyarch has made a fantastic multiplayer game.  I enjoy it even though i have my opinion on things that could be made different just as i'm sure you have yours.  Still, it's a bummer to see a whole class of weapons rendered useless because of abuse they've suffered in the past (and I admit that they WERE abused in previous games).  The draw to CoD multiplayer for me has always been the different play styles all being thrown into the same game creating a delightfully fun sense of chaos that i don't want to see reduced to 12-18 guys running around with the same 3 weapons.