Simplicity is divinity.

• Invisible walls:
  Good maps incorporate "What You See Is What You Get" (WYSIWYG).
  Unfortunately, Sandstorm is replete with objects, platforms, rooftops, rocks, terrain that seem reachable, but are not. This reduces realism, and induces frustration. Stop it, please. Recall CS 1.6 or UT 99. What you saw was what you got; nearly everything was reachable. Moreover, these game were also competitive; the nooks and crannies added to the skill gap, and the ability to 'explore' or 'trickjump' stimulated the imagination.

• Restricted areas & spawn protection:
  Similar to the explanation above. I frequently have no idea where I'm allowed to run. The latter sentence even sounds silly considering that Sandstorm should be realistic. Remove restricted areas, and incorporate spawn protection.

• Auto kick serial teamkillers
  Since NWI is adamant on disabling kick-vote, auto kicking serial teamkillers should be a reasonable middle ground.

I'm convinced that the more a game tries to control its players and maps to increase fairness and balance, the less balanced and fun a game becomes.