I think Snakedance is much more straightforward. There is an ancient evil that has awoken, it finds its way into the upper echelons of society from whence it can manipulate its takeover, the Doctor has to puzzle out what is happening, out-smart both the ancient evil and the petty bureaucrats and save the day. Kinda, on the other hand, has a lot more dream sequences and visions, the Mara's aims are unclear and its methods of control obscure since the society of the Kinda is much more alien to our own, pretty much everyone with the exception of the Doctor, Adric and Todd is behaving in a largely incomprehensible fashion.

I don't think any of that is necessarily a negative, but I can see why, at the time people were just bemused and, as a result, didn't rate it much.