I've just watched the clips so here is my take on the week:
The theme didn't work well in the form it took, however I think it actually could have had potential if done differently. Some dances are American in origin - foxtrot was invented by Vaudeville performer Harry Fox and the quickstep evolved from that (and a number of other dances contemporary to that period). Likewise jive evolved from lindyhop and jitterbug. There is the Charleston from the 1920s prohibition too. Therefore using many swing era/crooners tunes like those of Frank Sinatra would have produced suitable music and still been essentially American and also sticking to more of those dances listed above would have fulfilled the theme. They could have just stuck to decorating the studio in the American flag?
Anyhow to each couple.
Ralph and Karina - samba.
I really felt for them as they seemed puzzled with how to deal with the theme. Their music just could not be shoehorned to have a samba rhythm so they were immediately at a disadvantage. Karina did a great job of trying to get samba choreography in, but it was never going to look right when danced to that music. I was completely underwhelmed. I think he could be on dodgy ground this week in the voting.
Chris and Cheryl - Viennese Waltz.
This was a good attempt. I felt like I vaguely knew the music but sounding different so I wondered if it had been re-written to accommodate the VW timing. He had a good attempt and tried hard. His posture was good but he was flat footed in places. Quite a lot of true VW content which was good to see.
Petra and Dmitry - Quickstep
Petra always looks a bit wobbly when she dances and she has an odd posture. I think this is because she is too tall for Dmitry though she possibly has a wobbly core. Her dance was off in places and some footwork was untidy. However it was a good attempt to very fast music. Music was nearly suitable but the singer really murdered Elvis and it didn't quite sound 'right'.
Romeo and Chelsie
I thought Romeo's attitude was a bit better this week. He seems to be taking the competition seriously now. Frank Sinatra - New York New York is a proper foxtrot but again the band/singers murdered it and made it a little fast. However this pair were the pair where afterwards I thought I must have watched a different dance. I thought it was dreadful. The foxtrot in hold seemed very bouncy when it should be smooth and gliding. I did not like the choreography at all, and then the judges raved over it!
Hines and Kym - rumba
This music worked but was a little fast. I thought Hines picked up his feet a bit too much and I couldn't see as much hip action as Carrie-Ann suggested. There was a fair amount of content though mostly of the lady waft around the man sort, except for sliding doors which were repeated a couple of times. Maybe a point or two overscored.
Kirsty and Maks
Music

This was a nightmare for Maks to choreograph. Fair play to him for trying to appease Len by putting in some official foxtrot, alas it looked so forced as it went where it would never fit. Completely unsuitable music. Kirsty looks down a lot. She needs to hold her head up.
Kendra and Louis - Foxtrot
This dance was ridiculous! It was a quickstep of sorts, there was no foxtrot content - it may have had a reverse wave (foxtrot step) shoehorned in but I'm not sure if it was or not. I think Kendra had QS before(?), but otherwise I don't know why they didn't make this a quickstep and be done with it. So little was actual official ballroom choreography anyway. She was however dancing a lot better with more confidence and better posture.
Chelsea and Mark - samba
This was so much better - the dance of the night for me. Mark's choreography is so much better when he plays it straight. The samba rhythm fitted into the song reasonably well, not perfectly but better than some during the night. Chelsea had good hip action and her technique looked quite good for a beginner.
Just one final point. A lot of the costumes were dreadful and I'm not sure it helped their cause. The American flag dresses/suits (

) were offputting and I really feel strongly that ballroom dances should not be danced bare chested (even if the owner of the chest has a well kept body

). Also Hines' suit probably hindered his movement for rumba.