I'll go with the plot was pretty weak with a bunch of holes. But that's it. If you didn't have fun playing this single player, you either don't like shooters, or you're playing on a crappy ass TV. This was probably the closest a video game has actually made me feel to being "in the game." It was stunning.
You can skip talking scenes after the load up, press start. And the other scenes you can't skip are so short it doesn't matter because you need a break between intense battles. How can you complain about the last scene, your 5 minute scene is actually only about 2 minutes, and it's a pretty sweet fight, those dudes threw some hard punches.Sure, the game ends after you get in the raft, but it's still a good ending.
Yes, you can explore levels to an extent. That's how intel is found to fully complete the game, just don't trigger the next wave. But no, it's not an open world environment, why would it be? It's COD for god's sake, a story game, not a free world experience.