Basically, I played this game all day yesterday and my overall impression: it's awesome and it doesn't resemble CoD in the slightest.
I could see why people might think it looks like CoD when you watch gameplay videos (I know I did), but once you get into it, there's not much at all to use to directly compare it to CoD--this could be a very polarizing game for fans of the series, but for the general gamer, it's a good thing.
CoD was all about getting an enemy in your sights first and almost all the time, that would leave the person with the crosshairs on them with little-to-no chance of winning the encounter, but in this game, while there is a definite advantage to getting the drop on someone, it's not so overwhelming that you can't stand a chance. Your human characters (or: Pilots), have much more health than they did/do in CoD and have many more options in terms of maneuverability to avoid being taken out so easily. The other main difference is that while CoD was all about rewarding people who play well with powerful tools to kill more people than they already have, Titanfall tends to balance this out better so that you're never absurdly too powerful to fight against.
I know there was a lot of negative criticism in this thread about the lack of a real Campaign and if that's something you want in your games? Then you should definitely skip this, because the "Campaign" (used in the loosest of ways) in this game is skeletal at best. You do have to go through it to unlock some things and I did, but it's so inconsequential to the whole part of the game, that I don't see why they even bothered to structure it the way they did. But, I was just in for the Multiplayer, so I personally couldn't care less, and the Multiplayer, is in fact, very damn fun.
If people want to know more about the game I will be happy to tell them, but that's the longest post I have typed in a long time and the use of paragraphs has left me exhausted.