Mario and Sonic at the Olympic Winter Games
has many games (listed below) and play options so there's something for everyone. It also has variety for different situations, such as playing alone, as a team or against others, which make it a great all-around game.
Alpine Skiing (Downhill and Giant Slalom)
Ski Jumping (Individual and Team Large Hill)
Freestyle Skiing (Moguls and Ski Cross)
Snowboard (Halfpipe and Snowboard Cross)
Speed Skating (500m, Short Track 1000m, Short Track Relay)
Dream Ski Cross
Dream Snowboard Cross
Other "Dream" events are unlocked as you play. These involve variations on the main events and some new ones. In the Dream versions you collect and use items, face obstacles, use different tracks, etc.
There are also 3 "Party Games" that seem silly when playing them on your own but should be a fun way to play many events quickly with a group of people.
Multiple modes--Single Match allows you to select your events and choose Versus, Team Versus, or Co-op Play. Festival allows an individual or team of up to 4 players to take on events and rival challenges as assigned over 16 "days" of the Olympic games. This is like arcade mode. You can also check your records against others' on WFC.
Balance board option--you don't have to use the Wii Fit balance board but, if you have one, you can do 1-player games with it. It changes the game play and provides additional variety. (It's harder than the regular controls though!)
Multiple characters--the characters all have different attributes and special moves so it keeps the play interesting.
Many games--as mentioned there is something for everyone due to nice breadth and depth--and all ages should enjoy it. It's easier to unlock things than in Mario Kart. It even lets you accumulate points and "shop" for decals so you can customize your skis, bobsleighs and snowboard, outfits for your Mii, etc.
Controls--if you want to play something that actually simulates hockey moves, skating, etc. this isn't it. The controls are fun and pretty responsive but not similar to Wii Sports or Wii Sports Resort (although using the balance board helps.) Also, the instructions for Curling tell you to use a bowling swing but neither my boyfriend nor I can get it to work that way consistently. We've found that you have to snap your wrist and then it works fine.
Balance board option--a pro but a con too as you can only use it for 1-player games.
No Wii Motion Plus option--it would be fun if WM+ worked with this.