I finally got a chance to sit down and play this a bit and its pretty fun. A game that plays like a slower 3v3 Rocket League. I only played the solo mode so far but I imagine online is much the same.
The ball is "heavy" so it takes some doing to get it to move, though sometimes a bouncier ball comes out which changes things up. That only happened to me once so far and the enemy team scored in like 2 seconds so I didn't get to play with it as much. As you shoot the ball powerups will randomly pop out which you can pick up to use. Shield, faster movement, some other things I'm not sure about, etc. The shield is nice because it makes blocking the ball easier. The ball damages you when you touch it but not if you have the shield active.
You take damage from the ball and from enemy shots. There are some repair power ups on your side of the field that you just walk over to use when you're low. If your health goes to zero you are taken out of the match for 3 or 5 seconds. Your mech stays where you "died" and can still block enemies and the ball, which was real fun when we knocked out 2 enemies right in front of their goal so we still couldn't score. When you respawn its in the same spot you died.
Goals get progressively smaller every time they are scored in, making it harder and harder to win. I thought that was kind of a neat touch.
So yeah its fairly simple but fun. There is Solo mode which has one-off matches of a Challenge mode which is 5 matches that are supposed to get more difficult as you play. I havent made it very far in that mode yet. There is also local play and even a download-play option so even if your friend doesnt have the game installed you can play together. This is also nice for when the online servers eventually shut down for the demo. As long as you have it installed you can play locally.
There is a a kind of "achievement" system built in. I've only done a few and they unlock random skins. There are also skin unlocks if you have certain amiibo but who has those amirite? You can also unlock a "Training" mode which is the training for the full Federation Force game, which was kinda cool to go through. Only sad part is playing it you think "Man, they really could have done a full Metroid game on this system but didnt...