Must have:
Power, mass, CPU constrains in crafting
I loved the ability to completely customize your weapons/frame through tweaking the stats of what you were crafting by adding a pinch of this material and a smidgen of that material. I didn't like the interface that was in place for doing it.
What I would like to see for the crafting interface is the player determines what they want the final stats to be, and the game tells them what mats they need. Power, mass, heat, and CPU would go up as the stats go up, but could be brought down with better materials or crafting improved power source/CPU/heat sinks.
Customization is what gives the player a sense of ownership of their avatar, and part of what keeps them coming back week after week, month after month.
Must not have: Meta gears/classes
Not sure what you mean by "meta gears" but "classes" are a must. If you can't train to wear a different type of frame where's your horizontal progression?
I have a lot more to say on the theorycrafting behind classes, but this isn't the thread for it. I'll try to remember to link to the new thread from this one, once I make it.
Edit: As promised, link to
http://forums.emberthegame.com/threads/theory-crafting-mmo-roles.124/
I would like to see at least 8 basic types of frames, possibly with tech branches for specialization (for tier 2 (and above?)). (Though anything over Tier 2 would start become vertical progression, so that's probably not a good idea on my part.)