No gameplay-affecting rewards at all. Gameplay-affecting rewards don’t necessarily have to compromise the integrity of skill-based shooter gameplay but I haven’t seen them hit that balance while remaining significant. If you want rewards, non-gameplay rewards can be effective without taking that risk.
In ET:QW, the upgrade system had a number of negative hits on gameplay. Because upgrade progression shadowed what the player was doing and reset at campaign conclusion, the system discouraged player adaptation and playstyle experimentation over the course of the campaign. For instance, if a player focused on the medic class, their healing abilities were improved for the duration of the campaign. That discourages the medic from switching to any other class, regardless of if the current objective and team loadout called for another class. The system also rewarded better players with better stats like reduced weapon spread. I’m no great font of aiming skills but I can see reduced weapon spread stacking my firefights by the second or third map. Finally, xp allocation was imperfect with fairly useless activities like deployable farming rewarding large amounts of points. That damages the goal of using the point system to encourage player cohesion.
Brink’s upgrade system takes a largely different form but fails to improve on the flaws of its predecessor. Again, we can sum up the goals of this system as character progression and individuality as well as encouraging team cohesion via experience point allocation. Same problem with point allocation. Player base (size and/or pc servers) didn’t go along with segmentation via player level which gives clear advantage to high level players (time>skill). When every player is high/max level, the goal of individuality is broken because there was so many upgrade points to allocate and such a clear distinction between average and great abilities that players have the same abilities. This system also shares the problem from ET:QW of sticking players to certain classes they’ve upgraded. If you want to use this sort of system, first balance them and then limit the number of active (activated or passive) abilities per class, dramatically, so that players who have played longer don’t have more abilities but more choices. Obviously, that is not balanced, just not as unbalanced and has more player differentiation.
Could you clarify what you mean here?