I've been playing WoW since 2005. I pre-ordered Aion last summer, and got into the beta aswell. It was huge change graphically from WoW to me, it looked all awesome and I was waiting to see more zones.
I leveled like 3 different classes in late beta to 20-25's.
When the game finally aired, I even forgot the month (last autumn), I leveled one character to 20 and looked forward for the last 30 levels, which was mostly grinding... I though, this ain't worth the time as it got more boring and boring for me.
I think it's worth the try if there's a free trials nowadays, but I wouldn't pay without trying it first. Some like it, some not.