I'm thinking about how the "virtual pet game" series Petz is not really a game - there's no explicit win state, no explicit goals with explicit rewards, no endgame or game over. It's just a sandbox of you, some dogs and cats with a state machine based ai designed to convey personality (and part of that aliveness is that you can't control them at all - even when you train them, they may choose not to obey your commands, and this isn't treated as a fail state), and you interacting with and observing with the virtual characters:
The Virtual Petz characters are socially intelligent autonomous agents with real-time 3-D animation and sound. By using a mouse the user moves a hand-shaped cursor to directly touch, pet, and pick up the characters, as well as use toys and objects. Petz grow up over time on the user's computer desktop and strive to be the user's friends and companions. The interaction experience is non-goal oriented; users are allowed to explore the characters and their toys in any order they like within an unstructured yet active play environment. This freedom allows users to socialize with the Petz in their own way and at their own pace. This also encourages users to come up with their own interpretation of their pet's feelings and thoughts. To date the Virtual Petz products have sold over two million copies worldwide.
-- Andrew Stern, "Creating Emotional Relationships With Virtual Characters"
In addition, without modding to unlock debug tools, you are not given explicit information about a pet's mood, thoughts, or physical needs. The developers wanted you to intuit these from the pet's behaviors, like you would a real animal:
Natural expression. When trying to achieve believability we found it effective for characters to express themselves in a natural way, through action and behavior, rather than through traditional computer interface methods such as sliders, number values, bar graphs or text. In Petz and Babyz the only way the user can understand what the characters seem to be feeling is to interpret their actions and physical cues, in the same way an audience interprets an actor's performance. We do not display bar graphs or text messages describing the characters' internal variables, biorhythms or emotional state. By forcing a natural interpretation of their behavior, we don't break the illusion of a relationship with something alive.
I've never played Creatures, but from what I understand, it's a more biology-intensive, sci-fi take on a similar premise. You watch virtual organisms learn and grow and breed and form relationships, and you intervene by interacting with them and their environment via a cursor. It's a "simulation," more than a "game."
There was a whole forum dedicated to "Virtual Life Games" from this era. There were other games like this. Virtual fishtanks that simulated all the complexities of maintaining a real-world aquarium, maintaining temperature and salinity and checking for signs of disease, with no reward beyond the simple pleasure of owning and watching fish as they swim in front of you. A similar game, but for finch ownership.
The forum doesn't exist now, and Wayback Machine doesn't have it. It went down before Wayback was as good at trawling the web autonomously as it is now. I can't remember what the names of those other series were. But it makes me feel something that Petz and Creatures are still being played, even in 2023.
I've never been able to get into virtual pet games of the 2000's and later, like Nintendogs. They were simply too... gamified, in presentation and mechanics. Different actions were discrete screens. Gameplay mechanics had explicit goals and rewards, things you were "supposed" to do to "progress." The pets themselves lacked in the sense of individual personality and agency I craved. Petz and Creatures, themselves, were gamified in their later installments, through the arbitrary addition of minigame segments and the like, before their franchises petered off at the dawn of the 2000's.
I wonder if what we really hunger for is the equivalent of that 1990's virtual life "simply a space to observe and exist in" feeling for other genres. When I play Spore, I wish I could simply exist as a creature forever, no goals above my head. I wish it could go on forever, within a more fleshed-out environment where things just exist in symbiosis with each other like they do in Creatures; not just to be gameplay objectives for a player to conquer. I wish other creatures were more complex, somewhat inscrutable (to the extent that all living things not oneself are) but capable to read complex thoughts into in if I imagine, like Petz.