I bought a tshirt and a couple of stickers which I was happy with. The packaging it came in was quite cool and made it feel better quality than the usual bubblewrap and brown cardboard that is usually associated with online purchases. I thought the tshirt might be terrible - it would be so easy for them to cheap out hard to raise the profit margin, but it's a really nice fitting one with good heavy fabric. I'd buy again, except that I just don't spend that much time shopping for clothes and prefer "no design" stuff to design prints.
If you dig into Redbubble there's often a pretty good range of stuff around any interest, tv show or whatever.
Where you say "didn’t look very artistic or special" I suspect that is the reflecting a weakness of their selling style: It wasn't special to you, but these niche designs are special to a small, specific group of people (think fans of some Netflix show). The Redbubble website relies on those customers actively and patiently seeking out the products and designs, rather than the usual model of selling to you through advertising.
