Well, I was wrong about having read Shamela before, and I can only think I've read a modern spoof of Pamela -- or perhaps of Clarissa -- as I have memories of enormous bottles of ink which are required to enable the heroine to continue her voluminous correspondence, and of her still writing (always in present tense) while being tossed in a small boat going over rapids or some such lunacy.
Anyhow, Shamela was very clever piece of writing, taking incidents from Richardson's Pamela and inverting them, so the naive and virtuous Pamela is here portrayed as a shameless and deceitful semi-prostitute who only pretends to innocence in order to trick Squire Booby into marrying her. Not exactly concise and to the point, but relatively short and it never overstays its welcome.
Joseph Andrews was something of an odd beast. It feels as if it started life as another satire on Pamela, as Joseph is her brother and is also virtuous beyond belief, which at the time no doubt appeared ludicrous in a young man (though I'm not sure if it's meant to be an attack on the double standard of male and female chastity before marriage). However, it spins out into an extended picaresque adventure with minimal plot and a great many digressions.
I've also started Tom Jones, and I've got 3 chapters into Book Three, about a tenth of the way through, but I've put it down for the moment to read some SFFs.