The first area I’m going to tackle for the PvE Sandbox is combat, as I think it’s the glue that holds everything together and really sets the tone for the type of game you are playing. It also fuels other systems, and so I believe it’s a good starting point.
Basically, think Mount and Blade or Darkfall. So no tab-targeting, each swing hits or misses based on where the target is vs a dice roll, and things like momentum, weapon reach, and area hit all come into play. I’d also add friendly fire (controlled to prevent griefing, so only when facing mobs and other restrictions), as this really helps control zerging (somewhat anyway) and curbs other cheap tactics.
One goal would be to keep the number of key presses needed to a minimum, so combat comes down to who has better tactics and reactions rather than who has configured their UI to account for the 20+ actions needed. To this end I would remove magic as it’s seen in most MMOs, but not to the extent that M&B does. Basically the world still has some magic to it (floating platforms, monsters, teleports, some kind of healing, etc), but the players themselves can’t throw fireballs or toss out dozens of buffs. Special NPCs could, be they friendly or not.
Since the game is a PvE game, monsters would have decent enough AI that they would drop back, dodge, and use cover. Nothing mind-blowing, but above the usually “run into your sword” charge that common MMO mobs do. Lots of other areas have evolved in MMOs since 97, it’s time for AI to do so as well. The point is to make each encounter challenging enough that you have to focus and react, but also simple enough that every fight does not become a raid boss effort. The more special the encounter, the mob would not only have increased stats, but also increased AI, rather than having a more elaborate script of abilities.
Ranged combat would be limited to things like bows, crossbows, and throwing weapons, and ammo would not be unlimited. The cost of basic ammo would be low, but players would be more limited by how much they can carry and when they are able to resupply. Ideally if you and some buddies are out hunting mobs, you would save up your ranged ammo for special occasions (getting an advantage on a tougher encounter, for instance), and use melee for common stuff. The crafting/itemization post will cover this in greater detail, but basically all items would suffer wear and tear in the game, and eventually everything breaks, so what you bring out is always a consideration rather than an assumed “use the best in slot you have” type of deal.
As for combat goals, the world would be such that player hubs are all friendly to each other (or at least non-combative), and all players fight against a common enemy faction. This factions goal would be, of course, world domination, and player actions would determine just how close that faction is to its goal. As the world would ideally be larger than what the player population could occupy, the enemy faction would be in control of different areas at different times, based mostly on where the current player population has chosen to establish itself (more on this in a different post about housing/cities).