Demo has 2 tutorial missions, 1 campaign mission (a historical battle, not the overhead board game style campaign in the full game) and the option for skirmishes/multiplayer.
I played through the tutorial/campaign mission and it seems pretty fun. Its definitely designed in the same vein as Kohan, units come in companies, resource collection is fairly similar, supply zones, etc...
The differences from Kohan are pretty major though:
1) Companies are pre designed, no custom companies
2) Bases are built in a more traditional RTS method, not the settlement style of the Kohan games.
3) You generally have 1 base, but you dont seem limited by how many resource producing buildings you can have in that base, so the economy seems simpler then Kohan.
As for the graphics/UI its using the same engine as Kohan 2, so it looks pretty good and has decent performance. The explosions in particular look quite good, and watching infantry go flying through the air from grenades is always fun. The overall UI for the menus is taken right out of Kohan II and just given a WW2 veneer, as is the in game UI. A few of the interface elements are different, particularly in the base management area, instead of a general recruitment button you have to select the individual buildings to recruit units (so barracks for infantry, armor pool for tanks, etc...).
Overall it seems like a solid RTS, will have to spend some time with the Skirmishes to see what kind of tactics and gameplay are really there.