I personally think there is a lot of value in these things, particularly in cases where it's just impractical to go back to school/university or that tuition is unaffordable. Quite a few years ago I learnt software engineering and basic computer science through free, online resources (a few of which have already been mentioned in this thread), it got me a few successful interviews and eventually a job.
That was actually the first time I have self-taught myself anything with the aim of breaking into a field that had no experience with. It was difficult at the beginning because I had just quit the job I had back then and fell into depression for a personal, unrelated reason; but perhaps that was also the reason that I eventually had the drive and focus to get through what I would normally have found "boring" at the beginning — I had nothing better to do. The experience turned out to also be one that is empowering because now I feel like I could learn a lot of things by myself.
Not sure if it helps, but here are a few things base on personal experience of going through this type of syllabuses:
* Assuming that they are written by people who are good what they do and know what they are talking about, these syllabuses are usually to be followed through step-by-step unless explicitly stated otherwise.
* Different people benefit from different modes of learning. There is nothing stopping you from using auxiliary resources to help you to get through a syllabus.
* More often than not it takes a few reads of some text/attempts of an exercise for me to really understand something. In one particular case I read through a book three times, about half a year a part each time, before I felt that I really understood it; and when I finally understood most of it, I was only glad that I decided to try it again for a third time.
* I think it helps to have someone to talk to about what I was doing, it could be a close friend or family who doesn't understand anything about what you are studying. Alternatively, if what you are studying is "popular" enough and there are communities of people doing the same—get connected. Emotional support helps.
* I always try to interact with people who are at different skill levels. There is always a lot to learn from people who are much more experienced than I am; and explaining what you have learnt to someone less experience helps to consolidate what I have learnt.
* Focus is very important. Find what works best for your through experimentation: if you can sit through some given material for a couple of hours straight, great (but do take care of your health and at least get some stretches and water); if you regular breaks, that's also fine—just make sure you set an alarm clock and commit to getting back to it when it goes off.
On a somewhat related point, for freely available resources, I would buy a coffee or make donations where possible to people who devote their time to help others. :)
I hope you will find something that works for you! Good luck!