Suggest me some good manga

Based on your example of 20th Century Boys, try (if you haven't already):

- Monster

- Planetes

- Eden (which is great but the ending let's it down imo)

 

hold on

here:
sstudy
seduction
heaven(onion)
sports girl
hand play
sweet guy
my sister has amnesia
aki sora
household affairs
velvet kiss
she is young
sow
ghost love
himegoto - juukyuusai no sei fuku
a world that i rule
usotsuki paradox
h-mate
talk to me
yahalue
blade play
brawling go
kimi wa midara na boku no joou
daisuki onnanoko wa daisuki desu ka?
uwakoi
love parameter
will you do as i say?
club sodom
lady garden

these are also in my signature

 

I forgot these as they are completed.

Ares, different art style but I remember loving it.

Lucifer and the biscuit hammer, weird name but one of the few mangas I've reread several times. The story never dragged on for me and had a very good ending.

Akumetsu, crazy good story. Just avoid the authors other manga wolf guy something. Was decent but had some parts I couldn't handle and dropped it then. (Rape scene very detailed, akumetsu had none of that)

 

Spoiler: Y'all need jojo