I have extremely different perceptions of OSC's virtues as a writer.
(The following will include fairly harsh criticism of Ender's Game, and also major plot spoilers of course).
I loved the book Ender's Game when I first read it, when I was ~12 or 13. It was one of my favourite books of all time when first reading it. I thought it was deep, and insightful, and well-crafted.
On rereading it in my late 20's, it was much more disappointing than I remembered. It basically wrecked my memories of the book when I actually sat down and reread it. Major things didn't work for me, and overall the whole book... well, there were still a few good parts and neat ideas, but it fell from the 10/10 of my memory to more like a 7/10. Big things that bothered me on the reread:
The entire subplot about Ender's brother and sister literally taking over the world by means of persuasive anonymous blog posts was a hell of a lot more persuasive and believable when I first read Ender's Game, before I had actually spent any time whatsoever on the Internet.
Ender's ideas of strategy and tactics are mostly shitty and uninteresting and not really good. The Enemy's Gate Is Down is classic and memorable and good, but a lot of other chapters are really badly unbelievable, but I mercifully forgot about them before the reread shoved them back into my face. Consider Chapter 8's amazing 'innovation' to the field of Zero G Laser Tag. Do you even remember the amazing innovation from that chapter, that Ender is the first one to come up with in the entire school for geniuses who spend all their time studying tactics and strategy? Ender has the 'brilliant' idea, when fighting Centipede Army, of 'attacking before the enemy is ready'. He is apparently the first person, in this entire school for geniuses, to ever consider the idea of "what if we attack them before they're ready?". Seriously. From the book, Chapter 8:
From now on no one could take five or ten or fifteen seconds in the corridor to size things up. The game had changed.
In addition to the not-working plot elements on more adult inspection, I just found a lot of the book's writing was a lot less good, and there was a bunch of miscellaneous stuff that took me out of the book. For example, holy shit is there a ton of racism in this book! When I grew up as a white kid in extremely white suburbia, this didn't really show up on my radar at all. But now... this shit bothers me and takes me out of the book for no reason. In an earlier reddit conversation about this book, I learned that in the 1991 version of the book they edited some of the most extremely egregious racism out in later editions. Here's one of the changes they apparently made - via stackexchange
"Let's freeze a few," Alai said. "Let's have our first battle. Us against them."
They grinned. Then Ender said, "Better invite Bernard."
Alai cocked an eyebrow. "Oh?"
"And Shen."
"That little slanty-eyed butt-wiggler?"
Ender decided that Alai was joking. "Hey, we can't all be niggers."
Alai grinned. "My grandpa would've killed you for that."
"My great great grandpa would have sold him first."
"Let's go get Bernard and Shen and freeze these bugger-lovers."
was changed to:
"Let's freeze a few," Alai said. "Let's have our first battle. Us against them."
They grinned. Then Ender said, "Better invite Bernard."
Alai cocked an eyebrow. "Oh?"
"And Shen."
"That little butt-wiggler?"
Ender decided that Alai was joking. "If you didn't hold yours so tight it would wiggle, too."
Alai grinned. "Let's go get Bernard and Shen and freeze these bugger-lovers."
There's a bunch of other stuff in a similar vein of random racism, I don't know what else was edited out of the '91 edition from the original I was reading, but that sample should give some flavour of it. It's possible the '91 is a lot less objectionable in this way.
In addition, there's in Ender's Game a bunch of sex-essentialism about how Ender has a bunch of 'female' traits like empathy and understanding stuff, when comparing the reason for Ender's performance vs that of his siblings. This is less annoying than the racism stuff, IMO. But still weirdly egregious, and it can be viewed as a sort of prelude to the OSC political positions you discuss in your review.