First of all, I will declare my point of view. I have been playing MMORPG games for more than 10 years, being Ragnarok Online my favorite one. I know everyone compares this game with RO and I think that’s unfair, but of course there are a lot of features similar to what we only find on RO (and others totally different). After watching lot of videos and reading this forum for months I have finally played 25 hours this CBT and my character is a C2 Cryomancer lvl 60. So, my thoughts about the game so far (I will ignore lag issues and bugs related with being a beta test):
Class system
Probably the more interesting class system I have seen so far and the best feature in ToS. That being said, cause of skill scalling I don’t like some classes being weaker than others. I mean, even if you take 3 circles of a rank 2 class, it won’t be as strong as a rank 6 class (and more class are coming). I would love if all classes were capable of being viable endgame classes. Anyway, it’s not a big issue.
Stats and skills (damage)
Adding a point of STR or INT at level 1 adds the same amount of damage when you have 10 or 100 points on that stat. Also, leveling a skill only adds flat damage which means that pure damage skills you level up at low levels will always be a bad skill at higher levels. That lineal progression of damage is not fun at all. I would like my choices to be more meaningful. Most of skill damage comes from the skill, while stat bonus seem to add only like 20% of damage. I think skills should have a multiplicative bonus added with stats (something like 300 damage + 250% ATK or even just 500% ATK). With damage stats being so meaningless and skills being flat damage based I can guess most PVP builds will focus heavily in CON because the won’t lose a lot of damage (if you played RO, think about how many damage a Wizard could deal with 1 INT and compare).
Leveling system/path
I won’t write about rates or if leveling is fast or slow since this is a beta and that could be easily changed at any moment.
It seems like there is only one way to level up a character. You start always at the same place, do the same quests, go to the same places… This spoils the wonderful class system the game has. I would like to test a lot of classes but do the same work every time I roll a new character keeps me back. I don’t get why level cap should be 500. I would be happy with a 100 level cap even if the leveling is 5x slower but with 5x more areas to explore at the same range of level, so everytime I create a character I could try a different path and explore areas I didn’t saw before.
To sum up, the game have a unique spirit and that’s the harder thing for a game to achieve. But I think some of the design decisions should be reconsidered if this game wants to be something more than a grindfest game (there are too many [korean] games to grindfest for months and no one of them are fun).
I would like to hear your thoughts guys 

