Here are some randomly selected innovations of recent years that I think have set great examples for other games. These games may not have pioneered the features I discuss, but they're certainly popular representations of those features.
This will be a series that I update with further articles from time to time.
The oldest innovation I'll mention is Halo's regenerating shield. Many shooter games now have regenerating health, and I think it's a great system. It doesn't just eliminate rationing and enable a wider range of tactics. It also allows players to take more risks, take combat to the edge more often. It offers the thrill of barely surviving and beating the enemy just a moment before your own defeat. Regenerating health isn't always the best health system, but I'd use it more often than not.
Strangely, regenerating health seems to be strongly associated with guns. It could fit a fantasy game like Oblivion or other adventure games just as well.
Two features in Assassin's Creed stand out. The key to both in context sensitivity.
The first is the climbing and acrobatics. The context-sensitive controls are incredibly simple. Assassin's Creed is one of the few blockbuster adventure games that is truly friendly to people who don't play games often... yet the simple controls are not "dumbed down" and are just as enjoyable for seasoned gamers. The animations are elegant and fluid. And the open setting offers many fresh and interesting structures to climb and cross.
The second feature is the combat. Assassin's Creed has the best swordplay of any game I've played, hands down. Once again -- elegant and interesting. The simple, context-sensitive controls offer a variety of options without demanding that the player remember lots of button combinations or hit some random button at some random time. The same moves that are used against one enemy can be used against simultaneous enemies, but the flow changes. Granted, combat didn't vary enough in the first game, though it seems they're fixing that in the sequel. Batman: Arkham Asylum makes use of a similar combat system, and it's just as gratifying.
One potential for future context sensitivity is to make environmental structures, objects, and conditions more relevant. A single combat animation doesn't have to bound to a single result. A particular move can be more effective on some enemies than on others. One knockback becomes effectively a different experiences from another when one sends the enemy slamming against a wall and the other sends the enemy over a ledge. And animations for events like flinging nearby objects (like in Sid Meier's Pirates! swordfighting) can be well worth the extra work.
Spore demonstrated potential for procedural generation, the creation of content by code on-the-fly. Similar systems appear in Diablo 2 and Borderlands. The basic goal is consistently fresh gameplay and endless discovery.
Obviously, fresh isn't always the same as exciting or even surprising. But the existence of less-than-thrilling content can be made fun by context. Just think of the natural world. Not every animal or plant grabs your attention, but the plentiful existence of mundane things like squirrels and common shrubs makes other things more remarkable. And even the mundane can surprise at times. Likewise, few would claim Diablo 2 would have been better if item diversity was exchanged for consistent quality. Spore is not made dull by milder and more predictable creations.
Much more could be done in applying this strategy to setting. It's one thing to replay the same setting under dynamic circumstances. It's quite different to journey through a new setting.
Also, I'd like to see procedural generation applied to NPCs. I'm not talking about dilaog, which requires hand-crafting. But loyalties, motivations, desires and other driving conditions of character could be generated on-the-fly for a world's characters and beasts... made unique for every player.