I'd say Sammy is a natural progression for a youth player, he's better now than he was 3 years ago, physically and somewhat technically too.
Agree about Cheick, he's been up and down and then up again over the last three seasons.
Sissoko, he's about where he was at Toulouse/France before he joined, though playing on the right-wing isn't exactly helping him.
Agree to an extent, though Obertan had a smidge of potential at Bordeaux and even Man U before he became the monstrosity he is with us.
I'd like to add if you wanted some further improvements beyond our current squad, you could argue for Simpson, Perch, Ba and Cabaye. I'm not suggesting Pardew has a hand in any/all of them by the way, but they improved during their time here I'd say.
Cabaye was playing in france and he did make it to the champs league with a so called smaller club...so he was no mug before he arrived. Ba, had already proven himself to be a good striker at West Ham. Perch, maybe and Simpson maybe.