The gameplay is fantastic, the only problem I may have is if the level cap is at 20 I don't know if it will entice me to play on. Should have been able to level up to 70 or 80 at least imo
When you hit 18 it unlocks the ability to start getting legendary/exotic gear that gives you a +Light stat. Light starts increasing you over the level cap which is needed for raids and increased level difficulties (which can go as high as 28 as far as I can see). Bound to go higher in the future.