is priest actually usefull in this game? does he have any usefull support spells besides healing, like buffs that increase party members attack power and other stuff and are they even good?

Are you serious??!
Yes. They are probably one of the most useful priest classes compared to other games. They are exceptionally strong and can even solo themselves up pretty high. Plus you can use your ultra strong buffs on yourself-

well i was reading through this forum and only saw negativ stuff about priests.

There is some negative with all classes. With Priestes i would guess that it's if you go INT, you get strong magic and buff spells. But then you don't have a easy time solo. If you go STR then you get good mace skills but weaker magic skills.. and soo on

every mmo has healers/priests...i don like mages but, lest just say a world without healers would seem less bright-_-