Reposting my impressions here, because I guess it's more relevant. This is based on the Japanese versions.
You get one hat per game as a commemoration for downloading. Each hat is themed on the game. Each game has 'achievements' some of which you get Hat Tickets.
The opening to StreetPass Squad is cute and the 3D effect is subtle (I had to confirm it was there by closing my eye and adjusting the slider). You seem to get 3 shots with the same set of Miis, in the event of dying. Controls well, but slow speed (but, also the first level). It's basically a shmup, with the Miis acting as extra guns. You can rotate them around your 'ship' using L & R buttons while you play. Your score is ranked against other players you StreetPass with. It's fun and the world/story is fairly detailed for what it is. As expected from Good-Feel it's got a clean graphical style.
StreetPass Garden starts off much slower. The game looks really good as it's quite graphically detailed and has a nice overall style and the Miis animate really well. The 3D effect is less subtle than Squad, but still not the strongest I've seen. There are a total of 20 flowers you must collect to become a 'Flower Master'. You get your pick of one of three seeds from which to start your collection. A little like Pokemon I guess. Miis come up and water your seed until it grows into a flower. You can talk to the Miis and have them show you the flowers they have. It's very quaint.
StreetPass Battle has a basic graphic style since there's so many soldiers on screen at once. You choose an option, which I presume relates to your color/armor style, and then your castle. You have 3 choices; Japanese, Western, and Futuristic style castles. You cannot alter your castle type once it is selected.
It's basically paper-scissors-rock, but your army (based on the number of people you've Street Passed with), is divided into Hose-riders, Foot-men with spears, and archers. Horses beat archers, archers beat spears, spears beat horses. The Miis you most recently Street Passed with add more soldiers to your army. Iwata added 10,000 soliders to mine!!
Each round is against another district you're trying to take over. There appear to be 20 to complete. You have to select how to divide your army into the three divisions when you face each region. Presumably, a low-numbered section will not be as effective against a larger section on the opposing team, even if the attack is super effective. You can only use each division once per battle. Some of the soldiers you defeated will join your army too.
You get resources from the regions you conquer that can be used to upgrade your castle, but this also takes away people from your army. Going from Rank 1 to Rank 2 to shrunk my army from 11,700 to about 7,200. This game also has a ranking system.
StreetPass Mansion starts off with a giant hand grabbing you and pulling you inside the mountain. It has a simillar 3D effect to StreetPass Battle. Graphically it is quite well put together and quite spooky. You are told you need to get to the 30th Floor by finding the hidden staircases. You do this by setting 'pieces' that will become corridors, which you will automatically walk down.Pieces are given to you by Street Passed Miis. You can rotate the pieces in 4 directions, like tetris. If you combine two pieces of the same color they will become rooms, not corridors. You then walk through and open up any treasure chests in the room.
When you combine different colored pieces, a door will form. Sometimes, when the door opens, a ghost will attack you. You have a gun to shoot the ghosts with, but there are batteries that must recharge before you can shoot again (you start with three batteries). You can also block the ghosts. Combat is in real time. Your items/weapons get leveled up as you battle.
It's quite fun and seems like it might get tricky. Piece colors are, of course, based on the Mii's colors.
---
Overall, they're pretty good so far. Garden is the worst, but it's charm and laid back nature makes it tolerable at least. It's certainly the least game-y of the 4. Maybe that's the point of it?
The other three are quite fun and Mansion and Squad, in particular, I can see becoming quite challenging. The three of them are certainly more involved than Find Mii ever was just in their introductory stages.