From my experience the actual platform, while certainly showing its age, is surprisingly well designed and still very much relevant, despite SAP the company doing its best to replace it with something “modern”/“nosql”/“bigdata”/buzzword-of-the-day. I think that it would do good to many web-oriented developers to study how SAP/ABAP works, because it follows the web-style request/response + background tasks architecture since it’s inception. One interesting thing is that the low-level network protocol used by NetWeaver is ugly undocumented binary thing that you are supposed to use through binary blob, but API of said binary blob has very much the “POST random JSON somewhere and get JSON back” feeling.
For the ERP itself there are many people downthread saying exactly same thing: the ERP works and is well thought-out. And almost always breaks horribly when you start to customize it to match your random ad-hoc business processes.
I loved the rigour of the thing, I trusted it.
I don't think it should surprise anyone that SAP makes mistakes and/or that ERP systems are hard to implement. SAP in particular is an absolute monstrosity. I don't just mean in terms of size either. I can't help but think about that Nietzsche quote about the abyss.
SAPs systems should become textbook examples of tech debt left to accumulate, of what happens when systems are allowed to grow in whatever direction is useful at the time without any thought for the future or proper design. This isn't very surprising either since I can't imagine that there is any group of human beings on Earth that is capable of understanding SAPs systems to the point where they could extend it safely.
SAP also takes the NIH syndrome and makes it a core value. Everything they make is worse than that other technology that accomplishes the same. See UI5 - it's like they traveled back in time and hired a CS freshman in the late 90s to develop it.
When they don't have the expertise to create a copy from scratch, they just use the competitors' solutions and wrap that in their own marketing. They want you to only use SAP stuff.
The figures mentioned in the article about how important SAP is to the world's economy and logistics should scare the living shit out of anyone.