As I said in response to Geoff's post about MMOFPS games, I don't think combat needs any goals if it truly is engaging.
I don't mean that goals are not necessary to gameplay. They are, of course, regardless of a game's genre and style. But good combat can be enjoyed for its own sake.
Halo offers players a clear goal: reach the end of the level to advance the story. Yet players are generally more focused on enjoying the battle at hand than moving forward. The same occurs in LOTR: Battle for Middle Earth II, Star Wars: Battlefront, Street Fighter II, Neverwinter Nights, and many other great games.
Sure, maybe your MMO isn't just about combat, and a depthful and dynamic combat system (which includes fun, dynamic enemies) requires a good bit of time and resources. Games like Halo and Street Fighter 2 can concentrate more exclusively on battle. But if the majority of time playing your game involves fighting (as in most MMOs), then there's no excuse for a lackluster combat system (as most MMOs have).
Grinding is the obvious result of focusing on goals to the neglect of the journey. When the journey is basically just filler between goals, I consider that disrespectful to gamers.