Army Corps is fairly barebones, I like to think it's been made this way to meet the launch window and if a sequel appears that it would be more fleshed out.
The only thing it kind of reminds me of is the underground/cave levels from Pikmin 2. You move from small square area to small square arena fighting enemies to get points/collect resources, and every so often a boss will show up. You are ranked Gold/Silver/Bronze at the end on overkill points, goblins lost and time (there may be something higher than gold, I'm not sure). I like the overkill scoring, you get points for killing an enemy with as much force as possible, so where you only need 20 of the sword goblins to perform an execution on a floating eyeball, if you manage to get more than that on his back and perform the execution you'll get a extra points for each one.
I've encountered 3 kind of gobins so far, Sword, Spear and Magic. Sword Goblins seem to be the strongest, Spear can do a dash attack, and Magic have a ranged attack. Circle Triangle and Square switch between using the respective types and X is dodge. You can use each class to attack normally by pressing R and use their special attack by holding L and pressing R. In the case of the sword guys you can throw them much faster but you can't move freely only dodge, Spear guys will all attack at once, and magic guys seem to give you a wider view (I'm not too sure what the advantage is aside from that)
So to get a good overkill point you can use the Sword guys special move to throw a lot on the enemies backs, but you'll be more vulnerable and the other two have similar risk/reward aspects.
You can collect body parts for the dead enemies and rubies(?) which let you buy new armour/weapons/items for you goblins use in the battles. Stages are often labelled by what type of enemy they primarilly have in them, so far i have seen Fire and Lighting. Magician Goblins also seem to have fire/lighting staffs, i haven't figured out if it's a case of fighting Fire with Fire or not (If an enemy is on fire you won't be able to use the spear/sword guys attack without harming your goblins)
There also is multiplayer, i haven't played it. The manual says it's for up to 4 players and you can share 200 goblins, 50 each at the start, but you can give/receive from other players while in battle - i think. It looks to be multiplayer for the main "campaign" too, though again i haven't tried it i just had a brief look at the manual last night)
It's a very simple game, but I have found it very addictive up until now (3 or 4 bosses in) it's very easy to pick up and play and suits the handheld format well in my opinion. I also find it impressive that it manages to have so much going on in the screen without any noticeable slowdown.