Are US national parks too crowded now?
The famous parks are still worth it, but the famous version is often the worst version. Go early, sleep close, choose shoulder seasons where sensible and do not build the whole trip around parking-lot optimism.
Answer
Crowds do not automatically ruin a national park, but they do punish casual planning. The busiest parks can feel like theme parks at midday near the most famous viewpoints, then become quiet enough to breathe if you start early, walk beyond the first stop, sleep nearby or choose a less obvious season. The issue is not whether Yosemite, Zion, Yellowstone or the Grand Canyon are worth it. They are. The issue is whether your plan gives them a fair chance. If every park visit begins after a long drive from a cheap distant hotel, you may spend more time searching for parking than feeling the place land.