yeah, I'll be honest in saying Modern Warfar = hasnt been played by me... actually any call of duty.
Closest I got was being in the CoD4 beta and that's it. I'm impressed but not rushing out to go play it. I've got other shittier playing games I'm more interested in playing.
Modern Warfare 1 & 2 are must plays if you're a fan of FPS games IMO. Very good single player modes (some annoyances with infinitely spawning enemies aside) and outstanding multi player IMO.
If you're not a big FPS fan, then no big deal not to play them.