I'm very impressed by the building system of the game. Where Elemental: War of Magic made multi-tile cities boring and strange, Warlock: Master of the Arcane makes them extremely cool and stuffed with interesting choices. The very limited building count makes each building a meaningful decision, and they included several buildings that greatly capitalize on this. Forts and mage towers as economically null choices that add extra defenses are great, as they trade off the inability to build any other building with that population point for some meaty defenses. The use of map-based resources as locations for special buildings -- not automatic buffs, or remotely-developed tiles -- is brilliant. The choice between a silver mine and a silver weaponsmith, for example, is a fantastic way to capitalize on their unusual take on special resources.
The traits and perks are fun and really add a lot to the individual units, more even than I remember that doing in Civ 5, though it had a similar effect there. It's not quite as compelling as crafting custom weapons and armor for your unique heroes, though.
The research system seems to be directly modeled after Master of Magic, yet feels a lot worse overall. They padded the spell list with multiple versions of the same spell, so you'll have stronger and weaker healing spells, stronger and weaker death bolts, and so on. While all the versions are useful, since the weaker one is cheaper to cast and sometimes sufficient, it feels awful to research a lower level version of a spell after learning a higher level one.
I have absolutely no idea what food does or doesn't do. When I had excess food, it claimed it was being sold into money. When I had negative food, it claimed my population was shrinking, which I certainly didn't notice. I would assume it indeed affects growth rate, but they really don't tell you enough to figure it out without having played a while.
Food is consumed as upkeep for both units and human population. Undead population consumes mana as upkeep. I never checked what the goblin/monster population uses, but I assume it's also food, or at least partially food. Surplus food is converted into gold at a 2:1 ratio. I don't believe extra food has any impact on growth rates, but you can use magic to accelerate a city's growth.
You can generate gobs of food if you devote a city to it, at least a human city, since there are a lot of food production multiplier buildings. They're very expensive though, and while that's mitigated by sales of surplus food, the city needs to have a very large base food to so much as break even on the maintenance cost. So even though food can be produced in massive quantities, and excess food is converted into gold, a pure food-based economy is almost always going to be inferior to a regular food-and-gold hybrid economy.
If you run out of gold and are losing money each turn, your kingdom won't automatically disband units right away. Instead, mana and even research will also start being converted into gold. This is bad times. For awhile my research was crippled and my mana draining quickly as the game started bleeding all my resources to pay for my armies and building upkeep. I never got to the point of running out of mana to see what happens then; I was able to acquire more gold reserves, then stabilize my income.