Can someone recommend me action adventure and fantasy manwha with nice or doable art style...

Try reading Trash of the Count's Family (=・ω・=)

here's my list (●'◡'●)ﾉ

action adventure fantasy (ies):
1. solo leveling
2. the beginning after the end
3. a returner's magic should be special
4. the omnicient reader's viewpoint
5. the advance player of the tutorial tower
6. god of blackfield
7. i am the sorcerer king
8. the great mage returns after 4000 years
9. trash of the count's family
10. solo bug player
11. the scholar's reincarnation
12. yeon lok heun
13. max level returner
14. chronicles of the heavenly demon
15. leveling up, only by eating!
16. dungeon reset
17. i log in alone
18. trapped in a webnovel as a good for nothing
19. max level returner
20. MEMORIZE
21. solo spell caster
22. mercenary enrollment
23. legend of the northern blade
24. ranker who lives a second time
25. reverse villain

Trash of the counts family

Strongly recommend if you haven't already read it: http://www.mangago.zone/read-manga/trash_of_the_count_s_family/?P0Yh

Then there's of course Solo Leveling ( http://www.mangago.zone/read-manga/solo_leveling/?9rVM) which has romance in it but that's not the focus and it's def not a harem.

There's also Noblesse, a classic:
http://www.mangago.zone/read-manga/noblesse/?gpGg

Oh gosh that's a lot O_o