Pantasy for instance.
I haven't built a lot of non LEGO sets but the Pantasy set I recently built was phenomenal. It was the retro computer I got as a gift.
There are also great alternatives for LEGO compatible toy sets. Some of them are even higher quality than LEGO.
The options to order online I have where I live are really limited. So when I was in Japan I went crazy. I'm really happy with what I managed to pick up.
These purchases were made in Gundam Base Satellite Kyoto, Gundam Base Tokyo and several Mandarake locations.
I haven't built a lot of non LEGO sets but the Pantasy set I recently built was phenomenal. It was the retro computer I got as a gift.