Militarily, I think, the Korean War saw China in positive light, as it showed itself capable to fight the UN to a standstill.
Politically, however, there were some clear negatives:
1. PRC was condemned as an aggressor state by the UN
2. The US decides to keep Taiwan out of PRCs reach. I am not sure whether it was the onset of the Korean War or the defeat of the Nationalist China that caused the US to change its intentions in regard to handing Taiwan over to China, but the Korean War certainly entrenched them in the position that Taiwan shall not be restored to China in the WW2 peace treaty.
3. Possibility of rapprochement with the US lost for two decades.
The US Would Never Accept the PRC Until It Runs Out All Other Options
Being the most populous nation on earth, China's rise means the rise of a political, economical, and military force capable to challenge the dominance of the US at world stage. Under the pressure of being challenged, the US would never accept the PRC until it runs out all other options.
1. PRC was condemned as an aggressor state by the UN
Then, who cares about these dirty US sexy strip-club performances?
While China is still labelled as an aggressor by the UN Resolution 498 of 1951, it is, in the meantime, designated by UN as one of the most powerful world peace defender because the UN welcomed China as a permanent member of its most powerful institution, the UN Security Council through UN Resolution 2758 of 1971. Looks like
only a UN condemned world aggressor can be a UN approved world peace defender, while trashes like ROC / Taiwan can only be designate as a no-one- wanted stinky dog-shit.
Is this a victory, or a defeat, or an irony, or an embarrassment to the UN, to the US, or to China, to ROC / Taiwan?
2. The US decides to keep Taiwan out of PRCs reach. I am not sure whether it was the onset of the Korean War or the defeat of the Nationalist China that caused the US to change its intentions in regard to handing Taiwan over to China, but the Korean War certainly entrenched them in the position that Taiwan shall not be restored to China in the WW2 peace treaty.
Your statement is problematic, at least in diplomatic terms. The US is in no diplomatic position to "hand Taiwan over to China". Taiwan is not like HK by any means. HK was leased to the British by Qing government. Taiwan was ceded to Japan by Qing govn't but was reclaimed from Japan's occupation by another legal Chinese government of the time in 1945. It has nothing to do with the US, diplomatically. The Taiwan issue now becomes an issue because the US realizes that it has to use every possible means, including use Taiwan, HK, Xing-Jiang, and South China Sea as chess pieces, to counter China's rise. With or without the Korean War, and either win or loss in the Korean War, the US will do the same thing to contain China's rise.
Your statement sounds like if the PRC didn't angered the US in the Korean War, the US wouldn't support Taiwan, Taibei then would automatically surround to Beijing. This assumption is against Chinese history. You may have to ask why didn't Zheng Cheng-gong's Southern Ming (郑成功-南明政权), which had no foreign support either, simply surround to Qing (大清)? In China's 2000-plus years history, very few regimes in exile chose to surround. The central govn't had to use force to quash the remaining regimes in exile as rebels. Since the practice of using force to kill rebellions has been used for the past 2000-plus years in China, so, I am confident it will be used again to wipe out rebels in Taiwan. It is a question of when, not why, and not if.
Your statement also sounds like if the US supports Taiwan, China then can't take Taiwan back by force. But this is a wishful thinking of Taiwanese. China can take Taiwan back by force regardless what the US would respond. If the US couldn't win the Korean War against the PLA seventy years ago, it stands zero chance to win any war against the PLA in Eastern Asia today. What prevents Chinese leadership from making the decision to reclaim Taiwan now is not China's war ability, but the issues that are related to China's job priority. Right now, eliminating absolute poverty is at the top priority, so, we know China will do nothing about Taiwan for now. After China finishes the job of eliminating absolute poverty in 2021, then anything could happen across the Taiwan Strait.
3. Possibility of rapprochement with the US lost for two decades.
Is this a childish naiveness, or a deliberate misinformation? You need only to have a quick look at Mao's article of "Farewell, John Leighton Stuart." (《别了,司徒雷登》) published on Aug, 18, 1949, in which Mao denounced US long-time aggression and political manipulation to the Chinese, you then know the US would never choose the CPC over the KMT. By the way, North Vietnam did not fight against the US in the Korean War, did the US award a rapprochement treatment to the N. Vietnam before the Vietnam War? And why not?
The US meddling in China's internal affairs has been long and deep. It started far before the birth of PR China, far before the start of the Korean War. And its meddling in China's internal affairs is aimed to harvest its imperialist gains from China, not aimed to increase Chinese well-beings. Choosing the KMT as the work partner in China is in the best interest of America. It chose to support the KMT in China's civil war due to its own political ideology and its own economic preference. It is impossible for the US to accept the Communist Party of China, and the PRC because it is politically incorrect. The fallacy of "Korean War caused China decades' good relationship with the US" is Taiwan's cheap political propaganda to belittle the importance of CPC's Korean War victory.