Eh, i tried rappelz recently, the potions have awefully long cool down time, not to mention it takes it forever to even heal you. They also make it so you have to do certain quests to progress with bosses that are hard to kill on your own, with little people in the noob town to help you. Thats the only thing i noticed, game play wise its pretty smooth some flashy skills and smooth graphics. A good thing is you can rent a mount from town for cheap which lasts a good 6 hours and its easy to get into the game.
As for Luna, i think your better off with this game, it has auto loot so nothing droped on the floor, it has a monster counter so after you reach a sepcific amount of kills you get free stuff. You also start with a beginner pack which gives u lame cash shop items. I think the quests are stupid tho, it just makes you run back and forth. The game play is a bit faster, doesn't matter which class you pick and the monster spawns are awesome you can litterly stay in one spot and grind there.
I havn't tried the pvp in neither of the games so i dont know about that.:P
Rappelz just seems better made to me. The graphics, gameplay, pretty much everything.
I played luna for a few days, didn't have enough to keep me going. Might have been better with a friend but other than that..nothing.
And I loved Corum back in the day. That was my second mmo that kept me hooked for longer than 1-2 weeks (first being runescape). But what they say about being dead, not sure haven't played in forever.
If Corum was "alive" then I would definitely recommend it.