Dynamic vs static customization

Mass Effect 3 multiplayer demonstrates how important quality is to customization.

It's not enough for the player to have choices. If only a few choices are appealing to the typical player, then you have enabled the player to choose a particular playstyle but have not improved replayability. If the player does not alternate between a variety of options, but rather sticks to one or two playsets, then the game is less dynamic and less perpetually exciting for that player.

In ME3 multiplayer, I am constantly rediscovering classes and weapons. Returning to a previous choice after playing with other choices makes that option feel fresh and even surprising.

AI and predictability

I played the Syndicate demo again. My character is level 7 now. I have probably played that same mission seven or eight times now.

What strikes me is how important the AI is to the replayability. I see players using the same weapons and skills, yet the battle is a little different every time.

In the movie The Ghost and the Darkness , one character tells another, "They've got a saying in prize fighting: Everyone's got a plan until they've been hit."

Good, dynamic AI forces players to adapt every time. It provides just enough predictability to enable strategy, but it doesn't let players anticipate everything.