I agree with you there. I honestly enjoyed the singleplayer in all 3 Shadow Infinity Ward games (MW3, Ghosts, and IW), but IW campaign was exceptional, best CoD campaign since MW2 in 2009 imo. Unfortunately, Shadow Infinity Ward has only made 1 good CoD game from a MP standpoint, MW3, and Sledgehammer assisted with the MP on it before becoming a full fledged studio.
Since I'm a single-player-first kind of guy, I actually prefer Infinity Ward, even though the studio has fallen out of favor with many fans. Likewise, I'm down on Treyarch (the fan favorite) because, in my mind, it hasn't made a great campaign since World at War.