I actually think Biosphere 2 was quite successful. As an engineering project it failed, but in terms of research it provided a lot of useful data.
The core issue with the design was actually concrete absorbing Oxygen from the interior air. That’s exactly the kind of issue you want to consider if we ever want to actually make sustainable habitats. Unfortunately, they never tried to make a biosphere 3, but I suspect that would have been far less ambitious yet more successful.
I think it's criminal how little research is being done in this area. Sustainable, closed ecosystems are very likely to be key to humanity's future survival and are a prerequisite for leaving Earth on any kind of long term basis.
The core issue with the design was actually concrete absorbing Oxygen from the interior air. That’s exactly the kind of issue you want to consider if we ever want to actually make sustainable habitats. Unfortunately, they never tried to make a biosphere 3, but I suspect that would have been far less ambitious yet more successful.