Well that was a pretty harrowing watch, I had to space it out over the week. My thoughts are:
The Portuguese police were utterly incompetent and Amaral is a disgrace, his insistence that his theory was correct ensured Madeleine would never be found. Swift action could have apprehended an abductor but everything seemed to happen so slowly. It wouldn't have taken long to get Madeleine out of Portugal either by car or boat. The roads must have been quiet at that time of night, I live in a city and there's barely a car on the road after 10pm, a call out for all patrol cars to stop and search vehicles never seemed to have happened. Likewise with coastguards. The whole investigation seems to have been an utter shambles from the start, I can only imagine how frustrating it must have been for the McCanns.
Do not understand why the dodgy men going around the resort claiming to be collecting for an orphanage weren't the prime suspects from the start, in particular the one who showed an interest in the woman's child and was found in her house on the day Madeleine went missing! Also appears to have possibly been the same man seen hanging around the kids play area on the beach. To me they and the resort staff are the most likely culprits.
Also I really think open borders in Europe has made people trafficking very easy, you can literally travel across several countries in a few hours with no checks. It really does seem to me that is the most likely scenario in this case. I really felt for the Spanish private investigator, the things he must have seen and as he said they can never been unseen. 
Lastly, I know a lot of people here in the UK, and on MN have issues with the ever growing increase of CCTV on our streets but ultimately it could prove very useful in a situation like this.
Would i ever have left my DC alone in a holiday apartment? No I wouldn't, I'm actually much more hyper vigilant on holiday than I am at home, but I have nothing but sympathy for the McCanns, they are living every parents worst nightmare, I can't even look at Kate without getting a lump in my throat and I hope to god they find their little girl one day.