Last generation was largely defined by the rising popularity of motion control, the rise of western RPGs and action-adventure games, the official saturation of the "bro shooter" (although that started to some extent with Halo in the 6th gen), the resurgence of local co-op and platformers, the rise of mini-game compilations, and towards the end of last gen, that reprehensible buzzword, "open-world".
With that in mind, I'd pick these as the top five:
1. Wii Sports - obviously
2. Wii Fit - the biggest push for fitness/well-being-based games and opening gaming to other audiences
3. The Elder Scrolls V: Skyrim - popularised the concept of "open world"
4. Brain Age: Train Your Brain in Minutes a Day! - similar to #2
5. Call of Duty 4: Modern Warfare - basically defines the modern shooter
Honorable mentions: Minecraft, Super Mario Galaxy, Dance Central, Assassin's Creed, Braid, Limbo, Super Meat Boy, Dark Souls, The Elder Scrolls IV: Oblivion, Grand Theft Auto IV, New Super Mario Bros. Wii, Uncharted: Drake's Fortune, Just Dance, League of Legends.
There are some other very good games out there, including some others mentioned in this thread, that I don't think are influential. Just because something is good doesn't mean it actually brings about significant change in the way games are made, whereas I feel like I can see some kind of impact that all of the above games had.
For the record, if I were to do a personal top five for the last gen, probably the only game I've mentioned that would make the list is Mario Galaxy.
