Well guys I just beat the core Space Invaders game in a whooping 34 minutes, it's quite fun but as you just noticed extremely short without the DLC packages, I'll start the DLC levels tomorrow. The subtle references to 1950's alien invasion and classic space invaders games are awesome. The game is pick up and play friendly and I like how the time and health meter are the same thing so if you get hit you lose time (you regain time by destroying buildings and enemies). The attacks are hilariously awesome my 2 favorites are the drill formation and the wrecking ball formation. Besides DLC the other WiFi functionality is leaderboards and this type of game is perfect for it.
If you are in a pinch the C button fires the super weapon which is essentially a huge mother ship towers over everything, you regain invaders up to the 100 invader limit and it fires a huge laser from the mother ship like in the movie Independence Day it's very awesome but your only limited to 1 - 3 super weapons depending on the level.
I only have 2 real complaints about the game. 1. To generate new invaders from you ship you can't move the UFO and shake the wii remote and nunchuk like a mad man 2. Even though switching through attack formations is fine with the B button I wish you could also do it with the dpad.
For the people that are wondering you can move the game to the SD card, you can move the DLC file to the SD card but it's DRMed so you can only copy it back to the Wii that purchased the content and the 1 block save file can't be copied to the SD card.