For me 5 stars only if it's intriguing. People's standards aren't at the same level so a story that is amazing to you may be mediocre to me. Personally an amazing story is one with good plot, character design (physicals and personality wise), good pace, and has structure (things happen with build up, it doesn't just happen for a moment of drama). If one of those is slightly flawed, it's a 4 star.
Most of the mangas I have read so far are 3 stars for me because they are just average. Shitty and pure bullshits are 2 and 1 star, when it's lovely and has something special I give 4 and the greatest are 5. It just makes no sense to rate everything 5, even the crappiest mangas here have 8,5+ rating even tho they are completely blunt and average and it is misleading too, the rating is such a useless and unreliable indicator
when rating a manga, do you rate 5 stars as in like "this is so unique and amazing" or "this manga is okay so no need to rate 4 stars"?