We literally travelled the planet in a day. The most varied glasshouse in terms of plants is the modern styled Princess of Wales Greenhouse, which to my mind contain most of the interesting specimens. There is a huge range of both temperate and tropical plants, including some of the biggest and oldest cacti in cultivation, carnivorous plants, and a large collection of orchids.
I think Kew preceded the Eden project by displaying "plants for people", and they have such plants alongside information about how they are used by humans. I particularly enjoyed seeing the chocolate plant for obvious reasons.
The large range of environments and plants makes this my favourite glasshouse.
However, for sheer beauty of construction, you can't beat the Victorian glasshouses. They house impressive specimens from all the continents of the world. You can also go upstairs and view the plants from the "rooftop".
There are some wonderful plants to look down on:
Some of the plants look more impressive from below:
Some of the outdoor plants are just as exciting as the indoor ones. I was particularly thrilled to get the following pictures of ferns unfolding:
There's a traditional walled garden, which for me is enhanced because every single plant is marked, so you can take note if you want to get one for your own garden.
All in all a plantswoman's paradise.