There is a great deal of puffing up Rider as this allegedly amazing character around here, but I was a bit disappointed. He's honorable, he's pretty cool, but he doesn't respect his master at all. Not that Waver commands respect...
In the end, Rider is just kind of an idiot. A pleasant contrast to the way 5th War Rider fought, but I think I preferred her style of fighting. Hers was the same way Kiritsugu and Maiya fight. I'm just not seeing how this Rider will be able to compete with Saber, much less Gilgamesh. His chariot charge is fast and powerful, but unless he can stop their movements, it won't do much good. We know that Saber's Excalibur Noble Phantasm is faster than any attack 5th War Rider could produce, and 5th War Rider's final Noble Phantasm was supposed to be one of the fastest. Gilgamesh is worse, as he typically prefers to stand on top of objects rather than the ground.
But Berserker, he was impressive. Where Hercules was raw strength and power, 4th War Berserker matches it with skill. Saber could receive his blows this time even with his boosts, but she was getting pressed back pretty hard. Anyone who can meet with Gilgamesh on even ground and get him pissed off enough to get serious is someone to be worried about. Not that the ending already didn't make it obvious who he is as Archie pointed out, but him going out of his way to attack Saber makes it pretty obvious now.
As for Caster, I'm guessing he thinks Saber is Joan of Arc? He doesn't seem like one of Saber's contemporaries the way Lancer is. Looks like this time, Merlin's little trick about Saber pretending to be male is going to backfire badly for her. Otherwise, Caster might not be so convinced she is who he thinks she is. Unless he's totally crazy, which seems pretty likely. At first, I kept thinking that Caster was looking at Iris.