[afavour]

There are off-brand budget Lego blocks available and they're (in my experience) all awful. Legos are very precisely manufactured to fit together smoothly, if the off-brand ones made in a factory can't replicate that then I don't have much hope for small-scale 3D printing.

[alexriddle]

The gap is reducing significantly - I have collected and built Lego for a long time and had this opinion but have recently discovered Lumibricks (formerly Funwhole) - excellent designs, and around 1/2 the price of Lego (but they all include lighting elements) and having put them together I can say they feel exactly like Lego. I believe there are other brands of similar quality.

[deng]

No sure what exactly you mean by "off-brand", but I have recently bought big sets from Mould King and Cada and they are perfectly fine. Not only are they cheap, I'd say the color consistency is even a bit better. The sets themselves are great, really creative, challenging to build even for older kids, something Lego stopped doing many years ago.