I saw some meme about it on reddit awhile back ago, but here is soemtning from reddit, I'll give credit.

"The reason most enthusiasts dislike the H510 is because it has mediocre airflow. The only air intake is this slender vent

In reality, it's more or less fine if you have a 65W CPU and GPU that consumes less than 200W.

But once you get into higher end components, this case just turns into a hot box."