The 20 is my favourite calibre by far. 'For me', it just delivers the right dosage in the right manner. It just feels 'just right' for hunting and this calibre have produced countless hunting results.
Now, this is not to say it will be right for every shooting situation nor right for what all shooter expects. It is not a magic bullet that some expect. Like any other calibre, there is no doubt of its potential accuracy so long as you pair it with the right pellet. Even an Olympic target rifle will perform badly if it does not like the diet so don't skimp on pellet testing.
The biggest problem for many is having to retool and restock on many tins and type of pellets. Pellet type manufactured and shop choice is now extremely limited. Add to that tins are not cheap making entry a seriously expensive commitment which then lead to magical expectation. Fortunately although there is limited pellet choices, they do work very well.
I do have a hw100kt in 177, and 2xhw110k in 177 &.20cal. The hw100kt is a fabulous gun but on the heavy side. It has the lighter A&M aluminium cylinder fitted. I prefer to take the 110's on a hunt as they are far lighter and still do a great job. Of these 3 guns, my hw110k/20 is the favoured gun; equally accurate but with a more confident knock down.
I have heard great feedback from several members owning the hw100/.20cal. Do a search and you should find their views.