Stormfall: Age of War
This is one of the facebook games I’m playing. It’s free to play but it’s one that is greatly assisted if you pay for some in-game currency.
It’s a war game, as the name suggests, so you have to build up your castle with resource buildings, research buildings, defenses and so on, then send your troops out to attack and unusually defend NPC settlements. I’ve not seen many games where your defensive troops are also allowed out to play.
It has a skill tree and a number of troop types. You can even trade scrolls if you have duplicates or need a specific scroll more than the one you have. The scrolls are then used in varying amounts to unlock a new skill that you can then train.
It does rely on a social network as many do these days but not as heavily as something like Farmville. It does however remind you of this every couple of minutes with what soon becomes a very annoying full screen popup that you have to close to continue playing.