I wouldnt say its let down yet, it all depends on what they are going to do to fix the major problems:
1.) Linear Progression - Honestly to fix this issue they will have to rework the maps. Why do i have to run in a straight line in each map? Cmon, do it like how RO had their maps and make about 70-100% of the map explorable, not just narrow paths to a field to another narrow path. You know who else had this problem? FFXIII
2.) MUH GRIND - Grinds occur when players have nothing to do for their level. Questing is one alternative, but you only get so much of that. What else is there? Item farming, waiting a few hours for a dungeon boss, dungeons with 5x caps and socializing. We need more interactive options to help level up as well. Add in a battleground arena to pass the time or hold bi-daily events like defending a town or attacking a monster village.
Once these two things are addressed this game will blossom, content takes time so I don’t care if they stop the process to fix these core mechanics of the game. With how the game is set up physics wise there is MUCH POTENTIAL to this game, it just depends on how good their programmers / thinkers are.