This is from my previous accord, a 2005 2.4 5mt. It had about 150K miles at the time of this picture, I had only changed the oil once since buying it, I used a semi-synthetic penzoil. So this cleanliness is thanks to the previous owner. I did not clean this! Got it from a dealer, so had NO service history whatsoever. But whatever they did, it worked good!
Before cleaning
After cleaning
This is my brother's 2001 mazda miata 1.8 5mt. It had maybe 135K miles at this picture. Haven't owned it long, so this is from the previous owner.
My car! 2006 Honda accord 3.0 V6 6mt. Also 135K miles at the time of picture. And yet again this mess would be due to the previous owner. After running through my 2nd PP change, I may pull the covers off to take another look.
This little one was all me! This is a Huashengtaishan 142F, a Chinese clone of a Honda GXH 50. Complete estimate here, but I think this was around 50 hours on it. I don't remember what oil I used. But I have Mobil super 5w30 in it right now. I recently pulled the whole thing apart to see how the casting quality was, and maybe to improve it, and the piston was completely covered in carbon. The exhaust valve (adorably tiny!) had a layer of carbon starting, so I cleaned all that [censored] off. It's back together now and has stronger compression than ever before.
I have pulled the valve covers off of many more engines, but I don't always get pictures. I always check/adjust the valves if the cover comes off though. I hope OP did the same.