This is a tough game for me to judge. Does it succeed at being a balls to the wall action thrill ride? Absolutely. Modern Warfare 2 is bigger, louder, more savage, and has much more variety than Call of Duty 4 did. Does that make for a strictly better game? Not at all, in my opinion.
Call of Duty 4 was a major improvement over its predecessors in the storytelling department. It offered a clear geopolitical thriller narrative that immersed players in events instead of simply showing them in cutscenes. The game had only a few important characters, just enough to drive the plot forward. Modern Warfare 2 takes a different approach, this time putting you in control of 5 different characters throughout the campaign, with multiple competing villains, and events that take you to every corner of the Earth and beyond. However, the plot moves so quickly that you might not notice how little sense everything makes. Why is Price in the Russian gulag? Why exactly does Shepherd want to rescue him? Because it makes for a cool looking level, that's why. Consequently, most of the levels feel like they were designed as cool set pieces first, and logical parts of a coherent story second. Character motivations are often unclear or unbelievable, with major leaps in logic required to accept a lot of the story’s events.
Modern Warfare 2 takes the same approach in the gameplay department, being bigger and more chaotic in every way possible. There's more weapons, diverse locations, and gameplay gimmicks. However, this results in an experience that doesn’t feel as tightly crafted as Call of Duty 4, and left me feeling disoriented as I jumped from one level to another. In the first act alone you go from an on-rails shooting mission in the Middle East, to a stealth mission in a snowy mountain range, to a terrorist attack in a Russian airport, and ending with an absurd shooting gallery type mission in a Brazilian favela. These transitions happen so quickly that it's easy to lose track of why you're on these missions. There's little continuity between missions, as you frequently switch between characters and locations, leading to uneven pacing. In contrast, Call of Duty 4 had the player swap between characters, but they gave each portion of the story time to develop before yanking them out and dropping them in some other part of the world and presenting them with a new gameplay hook.
Modern Warfare 2 is visually impressive and delivers over the top, blood-soaked and action-packed gameplay. However, it sacrifices narrative coherence and tight pacing compared to Call of Duty 4. It has plenty of memorable moments, but not always for the right reasons.