There is no special content that is only available to paying players.
You get to play the entire game when you download.
Sure...up until level 60 or so. If you want to progress past that, you better be willing to dive into the cash shop in one way or another. You either have to trade gold with someone to buy diamonds from them, or you have to use real money and buy diamonds that way. The "advantage"
is needed if you want to get even remotely close to endgame.
Not to mention that in the higher level zones, some degree of gear modding is required, as mob HP/pdef/mdef scales pretty high, as does their damage.
@ OP - RoM is very pay-to-win, in that the cash shop is incontrovertibly mandatory, but if you're willing to spend a long (and I mean
a long) time grinding up gold to buy diamonds as a free player, it's possible to get geared without paying. Putting some money in will help quite a bit, but money really doesn't go far in this game.
It's worth a try, as it is a fun game, but just be aware that after level 60 or so, it's a very steep climb to the top. Rewarding, if you make it, but it is time-consuming if you don't pay.