Favorite MMORPG
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DDO
I recommend that you try this game out. It's problem is that it has too much content
What matters
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Progression - you should always be progressing through the game. A gear treadmill isn't progress. Exploring new areas, mastering new skills (you master them, not your character), and so forth is progress. Once there is no more progress, a player will get bored and leave.
Interactive environments - static environments are very boring. The environment should always be a living thing. The environment may aid or help you in battle, etc. High level areas may have very difficult environments too.
Unique enemies - when dealing with enemies, be they politicians, other merchants, or whatever, those enemies should have unique quirks to them. An example would be having to deal with the shell on a giant crab. Furthermore, each enemy itself is unique.
In-depth gameplay - it's not about just killing things. A single-faceted shallow game like that is no fun.
Deep game mechanics - everything should be simple to do at first but be very deep. Easy to start, difficult to master. One example is a magic system that requires players to actually know the spells and craft them in real-time. Players would research new spells using a set of principles that define what spells are (similar to chemistry and physics).
Global relations - relations between cities, nations, kingdoms, empires, and so forth. A dynamic changing world.
Politics - Set dynamic (not static) policies for a given city. Relations with the people. Elections. Consider NPCs as well. A person should be able to dedicate themselves to being a politician.
Commerce - Global trade = bad. Should be able to set up shops and move between cities. A person should be able to dedicate themselves to commerce if they want to. Land, structures, items, whatever.
Artisanship - good meaningful crafting that actually matters (no gambling, no simple collection, I like to experiment in a more real-world type setting, meaning no combos! Do it all from scratch). A person should be able to dedicate themselves to being an artisan.
War - Actually join a military and go up in the ranks. Eventually lead battles and wars. Work with politicians, etc.
What's bad
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Grinding - no real gameplay, no real progression
Arbitrary Gameplay Systems - whether complex or simple, these are bad
Poor UI
Simple Gameplay - it gets very boring very quickly
Theme Park - yea... as bad as grinding
Suggestion
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Design your game around having no levels. Add levels or whatever you want in later on. This will ensure that you don't use levels as a crutch for progression. Do not use any leveling whatsoever for skills etc. Design your game around the player. You may have new items, but don't increase the power, just increase the utility. Once all of this is designed, you will then have a deep and meaningful game. You may then add levels
. The levels and so forth would then be used as a new feature, not as a crutch to substitute for real progression.
Please also keep in mind that if it's a save/load online RPG, players will likely repeat the content several times. As such, linear progression, puzzles, and so forth won't be very good. You need to get away from problem solving.
Furthermore, if you design your game around utility, strategy, tactics, and twitch, low level players will be able to play with high level players just fine ^)^.
Levels do give a strong sense of progression.
