Love this thread. In addition to the considerations mentioned about variety of animals, I'd add that a factor that I look for is a diversity of animal mechanics and in-game management options/challenges. For example:
Packs that include animals with a diversity of herd sizes, mating patterns, and breeding combinations.
Packs that include animals that have a diversity of traversable systems (swimming, diving, climbing, flying, burrowing, brachiation)
Packs that allow for a diversity of habitat constructions (large vs. small, shared habitats and interspecies bonus, walk-through options for guests, multiple biome choices).
Packs that include animals that can realistically include albinos, melanistic, or different color/fur types that can be bred for with the in-game genetics.
Packs that allow plants and enrichment items that can be retroactively used with existing animals (exponentially increasing our options, rather than just being stand-alone additions).
Some of these come about naturally by having diversity in species types. And others become more and more possible as more mechanics are added to the game (diving, burrowing, hopefully flying, brachiation and underwater). But a pack that met all the other criteria in this thread, but where all the animals could only be kept in monogamous, single-animal non-walkthrough habitats, for example, might bring less enjoyment for me -- even if all the animals were ones I really wanted -- than one that mixed up these gameplay mechanics as well.
Packs that include animals with a diversity of herd sizes, mating patterns, and breeding combinations.
Packs that include animals that have a diversity of traversable systems (swimming, diving, climbing, flying, burrowing, brachiation)
Packs that allow for a diversity of habitat constructions (large vs. small, shared habitats and interspecies bonus, walk-through options for guests, multiple biome choices).
Packs that include animals that can realistically include albinos, melanistic, or different color/fur types that can be bred for with the in-game genetics.
Packs that allow plants and enrichment items that can be retroactively used with existing animals (exponentially increasing our options, rather than just being stand-alone additions).
Some of these come about naturally by having diversity in species types. And others become more and more possible as more mechanics are added to the game (diving, burrowing, hopefully flying, brachiation and underwater). But a pack that met all the other criteria in this thread, but where all the animals could only be kept in monogamous, single-animal non-walkthrough habitats, for example, might bring less enjoyment for me -- even if all the animals were ones I really wanted -- than one that mixed up these gameplay mechanics as well.