Nothing more than an incentive to take your 3DS outside.
Now let's move to my complaints. First of all, you can only get 10 play coins every day, which limits both games to how lucky you are with streetpassing.
Second, you can only hire level 1 or 2 miis. To get higher leveled miis, you have to streetpass someone multiple times(everytime you streetpass the same person, his mii levels up in your game, starting at level 1).
Third and last complaint, the game limits you to 10 streetpasses(if you get 10, you have to use the miis to get more), and you have to use the miis you streetpass immediatly after you open the plaza, or otherwise you won't be able to use them.
The game rewards you with hats for your mii, which is cool.
Overall, not a great experience, and lacking, but it's just some free little mini games, so it's forgivable.
5/10
Presentation: The plaza does the 3D effect pretty well at some times, in both puzzles and Find Mii and the graphics are nice and mii-ish, in Find Mii. The music is pretty nice for what it is, but not great.
7/10
Story: The story for Find Mii focuses on your mii being kidnapped and you having to hire heroes to go rescue him/her. There's not much depth to it, and it's OK, but it won't entertain you and it's only an excuse for the gameplay. Puzzle Swap doesn't really have a story, it's just your mii walking, finding other miis, and swaping puzzle pieces with them.
6/10
Replay Value: There's some replay value to this game, since Find Mii has to bea beaten twice to get all hats, and Puzzle Swap has many puzzles. However, keep in mind that this can't really be played for over 5 minutes a day without a ton of streetpasses.
7/10
Fun: I didn't have too much fun with this, since I couldn't play it much daily, but at least it was something to keep me excited whenever I got a streetpass, so it does its job there.
7/10
Overall: This is not the greatest experience you will have(definitely), but it's a nice incentive to take your 3DS out, and it's free, so you don't lose anything with trying it out.