Persistent systems have become an effective way of smoothing out the difficulty curves of rogue-likes, and provide replayability and progression to many video games. Despite their popularity, there are ways to cause the player to lose interest in replaying a game.
Persistent systems provide additional content or mechanics that add to a game built on a run or match kind of design. This is not the same as having progression over the course of a 30 hour game. Persistence is usually seen in rogue-like or match-based games, where the player is expected to repeat content or a playthrough over and over again.
The point is that despite the overall design being the same, there is a fundamental difference in what the player will be experiencing on their 1st, 50th, or 100th play of the game. Popular examples of persistent systems would be the Binding of Isaac and Call of Duty's multiplayer progression.
When done properly, the replayability will keep the player coming back to a game and can also be used as a form of supplemental content in future expansions. As a different kind of an example, the multi-system design of XCOM would be a smaller example of persistent systems. While you are not replaying the game every few minutes, each time you unlock something within a system, it will change what you do going forward.
With all that said, there are some important considerations when it comes to when persistent systems work, or do more harm than good.
A common practice for persistent systems is to use incremental upgrades as a form or progress. Simply put, the persistence has to do with abstraction: More health, reload speed, jump height, etc. The problem is that incremental upgrades do not change how the game is played on each run. In order for the player to see the difference over time, they need to have meaningful upgrades to their character or to the game in general.
Oftentimes designers will intentionally make the player very weak at the start, so that the persistent system becomes a compromise. Similar to Metroidvania design, purposely making your game frustrating at the start is not good game design.
The whole point of persistent systems is that the game is already good, but these additions make it better.
One of the biggest tells of when a designer messes up with persistent systems is having the game balanced by them. I have played plenty of rogue-likes that make use of persistent systems by making the game all but impossible until you unlock enough items (or incremental upgrades).
Persistent systems are not meant to be tied to the game's balance. The issue is that it creates a situation that the player will perform runs to gather the resources they need to then make a "real attempt." Compounding this is when the persistent system is about consumables, or items lost when the player fails.
A good persistent system can help pick up the slack if the player is not able to win the game on their own, but it should not be a requirement to win in the first place. Most games balanced like this tend to focus on incremental upgrades for obvious reasons.
For our last point, I want to talk about another variation that some games have made use of. Instead of providing the player with set upgrades or growth, we have seen games use random upgrades as their persistent system.
When the player beats a map or wins a level, they are given random items that can be used on future plays. Two examples of this kind of design would be Warhammer Vermintide and Lost Planet 2. The idea sounds good on paper: The player gets something surprising as a reward for each play. Unfortunately, this is not a good example of persistent systems. First is the fact that it's not changing how the game is played on repeated runs.
Persistent Elements should change how the game is played, not be a requirement
The second problem is that by getting random upgrades, the player has no idea whether or not they'll actually get something of use.
Playing Warhammer Vermintide, there were plenty of times where my "reward" was something I couldn't use; essentially wasting the entire match.
Like the last section, when your game is balanced on this system for progress, it becomes a gamble on whether or not you can keep going up based on the unlocks.
Persistent Systems have become an effective part of any game meant to be replayed, but just like any game system, they require a lot of work to be done properly. If your game isn't designed around persistence, adding a system in at the last minute will not help anybody.
Can you think of other examples of persistent systems and how they either helped or hurt a game's design?