More quick impressions:
Really weird to see my Mii in a dress. You can equip hats, different clothes sets, and dances.
After going to the World Ranking section, I noticed that there is in fact a number ranking, currently Rank 1. (had this wrong from my first impressions)
Friend Rankings are in place (I imagine they're leaderboards), which is awesome. Hope some people on my friends list pick this up to have some scores to compete with. Go to Records > World Ranking > Personal Records Ranking > Friend Ranking.
Friend Rankings for: Marathon Endless ON, Marathon Endless OFF Score, Marathon Endless OFF Time, Computer Battle Knockout (Time), Survivor Endless ON (score), Survival Endless OFF (score), Jigsaw (time), Shadow Wide Time (2000%), Fit Endless ON (Planes), Fit Endless OFF (Time), Tower Climber Everest ON (floor), Tower Climber Everest OFF (time), Bombliss Plus Endless ON (score), Bombliss Plus Endless OFF (time), Course J, L, S, T, Z Beginner/Advanced/Abyss (time), Capture (time), Master Mode Endless ON/OFF (score), Master Mode Endless OFF (time), Sprint (time), Co-op Tower Climber Everest ON, Marathon Consecutive Tetrises, Marathon Maximum Lines, Marathon Consecutive B2B, AR Marathon Score, AR Marathon Time, AR Climber.
Of course you can look at Global Rankings for all these modes as well.