I spoiled the Good Ending by accident >.<
But I don't really care, as it's not the True one, and it seems too good to be true from what I read.
I'm reading a walkthrough to just see the Good Ending for UBW, although it's more out of sense of wanting to go through everything.
Since you asked for it, I'll give you my opinion on UBW:
The story was really cool, how it adressed the issue of idealism and realism, it kinda remineded my of the book Grendel where Unfurth (sp?) talks about being an hero to the nihilist Grendel. I was really attached to Archer from the prologue of the game, and was extremely dissapointed after so many cool characters were introduced, and then abandoned in Fate. I'm glad I learned after the credits that there was UBW. I loved how Caster went from being one of the weakest Servants, to an almost invincible one (I didn't die by her in the first one, so I didn't see Saber getting stabbed in the Fate story line). I didn't really get the teacher... I'll have to replay the game and read some stuff online, and I didn't really get Caster too, other than learning about her deeper intentions and love she had in her.
I loved Sasaki Kojirou. His character is a simple one. He's fictiotional, and has no Past or Future, and his sole purpose is to accomplish something during his short existence. So he wasn't just some annoying asshole that wanted to block Saber for the hell of it.
It kinda sucked for Saber, but that's only because her acceptance of her fate wasn't elaborated as long as Fate. She learned like the main character, that although she'll go back to her past, unrewarded, and left to die, and to add salt to injury, without as much hapiness as from Fate (although she said she still had fun), that her path was not a mistake. She also had some purpose and fruits of her labor, only wishing to allow her two Masters to live on and be happy.
It's kind of hard to accept and understand Shiro, but I managed to accept his argument. Although you'll never reach Utopian goals and ideals, you, yourself, should never be ashamed at not actually reaching the goal, and at least you end up being a good person. By being cynical in the start, your character itself becomes corrupted, willing to betray, hurt, etc. So don't be so obsessive about the physical fruits of your labor, but worry about staying true to yourself, and always being the good one, at least being the ideal perfect person yourself, even if you can't make the world and others the same way.