A few things...

1) It was amazing how well Constance's diversion plan at Calais worked. She just put on an overcoat and a feather hat and the Cardinal's soldier immediately proclaimed that it was D'Artagnan and took off after her. If D'Artagnan was known for his distinguished looking coat and hat then this might have made more sense, but I don't know how that soldier could have been THAT familiar with D'Artagnan's dime-a-dozen coat and hat.

2) When Milady DeWinter's coach was being hoisted by the war machine, why didn't she jump out immediately when she noticed that she was going up? She's spry enough to have been able to pull it off and it would have foiled their plan.

3) When Rochefort's ship shot the explosive cannonball into the Musketeers' war machine, why didn't Porthos throw the bomb out of one of the windows rather than letting it blow up inside? The fuse looked pretty long when it landed there...

4) It's amazing that within one year of getting DaVinci's plans for the war machine, not only did Buckingham produce a working model, but an entire FLEET of working war machines! Not only that, but the Cardinal was able to receive a copy of the plans and IMPROVE the complex and innovative design. All of this within a year.

5) When Milady DeWinter broke into the Queen's chambers to steal the Diamonds and plant the forged love letters, she killed several Musketeers. Why were the love letters discovered before the bodies of the murdered Musketeers who would have been making regular patrols, being relieved, etc?

6) How on Earth did Milady DeWinter survive her plunge into the English Channel?