I played both Twelve Sky 1 and 2 with my friend. We were pretty obsessed with it back in the time because we found a nice community from our country there.
Personally I prefer the second installment. There aren't much graphical differences between the two - if you don't count the better overall design of armors in the 2. However they are both pretty grind heavy titles and focused on PVP.
On the highest tier of levels - there are regular ones and master levels in the first one - the second introduced god levels - it took about a month of grinding for one particular level. So... it's really not for casual people nor anyone who lacks the time for it thus I'll be passing on the title this time.