@Manbearcat is right. I am speaking from the perspective of mostly challenge oriented play. However what I call character exploration is extremely important to me in roleplaying games. Character exploration in the sense of feeling what my character is feeling, making the decisions they would make, facing challenges that make me question who my character is, and having mechanics that reflect their struggles so I do not have to play against the game is vital. Game play that fits the fantasy of my character and making choices that impact the fiction based only on the fiction and mechanics of the game is very important to me.
Character efficacy is not overly important to me. Having tools to impact the fiction where the ways I utilize those tools determines how well I do is something I look for in any game I play. Some of my favorite games to play including Exalted, Legend of the Five Rings, Apocalypse World, Monsterhearts, and Dungeon World are
not balanced games in terms of character efficacy. In Dungeon World the Paladin is straight up better than The Fighter, but they both have different and compelling game play challenges. I often choose archetypes like the Savvy Head in Apocalypse World or Mortal in Monsterhearts that are weaker, but have more compelling game play. In the last game of Exalted Second Edition we played I went with a Resistance and Martial Arts oriented build in order to challenge myself to see if I could make it work when the meta of the game is built around The Invincible Sword Princess, a dodging and parrying build that is built around never being touched.
Generally speaking I do not appreciate spotlight balancing from either side of the screen. As a player I want to exercise my skill at playing to the fiction, mechanics of my character, and group communication/coordination to achieve the ends of our characters. Once a scenario/scene has been framed I want the GM to play the opposition honestly and act as a referee. As a GM I view it as my duty to frame conflicts that challenge the players and their characters. It's up to them to decide how to overcome those challenges. During play I as the GM am an honest advocate for the fiction and their adversaries. No one gets to decide how things go.
As a player thematically I am mostly drawn to the fantasy of playing warriors, men and women of courage and resolve that take up arms to achieve their goals. I want to play Conan or Achilles. However in modern Dungeons and Dragons I have usually found the game play lacking. I want to make decisions that impact how successful I am. I want my effectiveness to improve as I become better at playing a Barbarian, Fighter, or Paladin. On the other hand I have always found the game play of playing a spell caster more compelling. As I learn the game, get a better handle of spells, understand where they useful, what monsters are weak to each save I get a rush from being more effective over time.
What I want is that same rush while getting to live out the fantasy of playing a warrior. I want it for my players when I GM as well. As many of you know for a long time I was a real big Fourth Edition fan because it delivered on this out of the box when during Third Edition I had to resort to playing Psychic Warriors and Clerics to get that same rush even though it was not the fantasy I wanted. However over time I get disenchanted with Fourth Edition largely because the choices I was making were not the choices my character should be making and mechanics that were overly focused on team play. I largely want mechanics that map to the fantasy of playing a fighter or Barbarian yet are still compelling in that they require skill to play well. They should not resort to things that have no direct correspondence with the fiction.
Speaking as a real life martial artist this should not be too hard. There is far more involved in a contest of martial skill than deciding who to attack with what weapon. It may not be something that mainline Dungeons and Dragons will ever do because it should be more focused on being accessible and simple fighters are traditional. It is a solved problem in some games. The Fifth Edition of Legend of the Five Rings provides a pretty compelling game play experience for bushi characters who interface with the combat system in ways that other archetypes just do not. Pathfinder Second Edition makes an attempt. I have only played at low levels so I am not sure how it will work out yet.
However I am interested in exploring ways to make this work in other games as well including Fifth Edition because there is a lot to love in Fifth Edition. Also because I have one group of friends that I will continue to play it with even as I branch out to other play groups.