To be fair if everything worked perfectly rather than being unfinished with several bugs here and there, it wouldn't have been a demo but EA release. Demo had everything that was expected for it and I had an amazing time creating vehicles and contraptions, despite the obvious issues, most of which are guaranteed to be addressed/fixed for actual release and would be better judged after that.
I do however agree with the baffling amount of stuff that you would've expected to have been caught immediately in QA, but was seemingly only caught in demo judging by the devs' blog about the demo aftermath & feedback. One of the most obvious ones (ignoring obvious unfinished / missing features) to me was the vehicles being very unstable due to too low mass and/or too high center of mass, which the aforementioned blog mentioned as if it was something that came up in the demo, rather than earlier in QA.
I cannot really vote on the poll as I don't think the demo was intended as a product and therefore I would find it a bit be misleading to state the obvious fact that for a product it would've been too unfinished, by far the biggest shortcoming to me being the lack of the ability to save and load entire contraptions without assembly required, which is something that EA is supposed to have, but which didn't make it into the demo. If the poll asked whether I enjoyed the demo, it'd be a very strong yes.
