Yeah it's pretty cool if you don't mind playing DM over and over and over an-...well you get the idea
Quest = PvE - fight mobs, sometimes they drop parts and some random shit>collect treasure to exchange for prize at the end>find and kill "special" mob to get key>go to gate>repeat at next map until you reach an "outpost">give treasure to npc>go through gate to continue playing through more maps/collecting treasure etc.
Mission = PvE - play through the stage fighting mobs with a boss at the end of each stage, usually has about seven stages including a bonus stage which is usually stage four or five.
Arena = PvP/BvB - Alpha and Bravo teams fight each other, each team has a "base" which gives you rapid fire bullets when you stand under it (bases can be destroyed thus the bvb element) , every time someone dies their team loses a certain number of points (depending on how powerful your bot is) and the team loses when their points are at 0.
In all battle types you do not recieve any exp or money until you complet the entire thing, except for quest where the mobs sometimes drop money in very samll amounts (5-50)