After reading GameInformer's preview of Assassin's Creed 2 and other tidbits, I'm excited about the game. The first game provided gameplay that was excellent but redundant. Ubisoft seems to be tackling the redundancy problem.
That said, I hope they don't focus on player dynamics to the exclusion of scenario dynamics. Player dynamics are the various methods of interaction offered to the player. Scenario dynamics are variations in all that exists with or without the player, like the setting and fixed events. One sort of dynamics is initiated by the player, the other by the gameworld.
In my gaming experience, the latter is more vital. Both should be present, but gameplay is better refreshed by environmental dynamics.
Bioshock offers players many choices in character development, weapons and strategy. But how eager were you to watch the same cutscenes, hear the same dialog, follow the same path, encounter the same enemies, etc? Scenario dynamics certainly existed, but player dynamics clearly received much more emphasis.
Oblivion is another example. Though the game had perhaps the best terrain variety ever, and dynamic weather to boot, too many things were static and predictable: enemy types and behaviors, NPC dialog, quests, gear, etc. I could approach the same adventure in a different way, but that's a mediocre, half-hearted thrill.
Scenario dynamics can include neutral factions/characters/beasts (will attack anything, the player or the player's enemies), visual events (like a flock a birds flying by or a piece of driftwood moving along a shoreline), variation in enemy AI, dialog variation, and gear variation. This is the adventure aspect, the unpredictable elements which the player must respond to.
It's not enough for a dynamic to create a new experience. It must be a meaningful and memorable experience. Wood that splinters under pressure from the player's bullets, for example, is a dynamic, but not necessarily a meaningful dynamic. A few crates falling apart or boards snapping in two as the player trades bullets with one enemy probably isn't going to leave a big impression. However, a huge battle with many enemies all around and splinters flying everywhere might be a fight to remember. If the player is able to shoot some support beams to drop enemies from a collapsing balcony, that's even better.
Anyway, I'm just saying, don't forget the environment and events out of the player's control when you're looking for possible dynamics to include. The unpredictable is usually more affective than the predictable.
Let me repeat an old point: replayability is what prevents gamers from trading in their games and forcing you to compete with used copies. And it increases value for gamers, because our games have lasting value. It's nice when we can revisit old games the same way we revisit old movies on DVD.
The games that earn my loyalty to a series or brand are the games that last for months.