The tapioca balls are actually very tasty, but need to be freshly prepared. Shops with high turnover or dedicated boba drink places tend to be better for this. Once the tapioca balls get to be day old, they do develop a very slimy exterior.

Also, I'm not sure that chocolate tapioca makes a good flavor combination. I personally like the classic tea infused flavor--it matches the milk tea drink a lot better.

That said, everyone has different takes for texture/flavor. The tapioca balls should be a firmer, chewier version of agar agar or jello.