[Edi]

Vladikus:

Single player is challenging enough. Out of 10 games, depending on how careful you are and how lucky you are, playing against Knight level AI (power level 4 on a scale of 1-10), you can expect to win maybe two or three. A lot depends on how lucky the AI gets and if it survives the early game, where random instances of bad luck have a greater chance of wiping it out.

If a Knight AI gets out of the early game, it's liable to bury you up to your ears in stuff if you didn't manage to expand quickly. Depending on what class it plays, of course.

Note that a Knight level AI only gets a 50% income boost (the bonuses affect all income, gold iron and special resources, possibly also trade points). The reference level AI is Jester (level 2), which has no bonuses or handicaps.

Crank the AI up to Emperor (level 10), which has a 500% bonus to income and you won't know what hit you. Or you will, when you realize that the massive army you just barely defeated by the skin of your teeth was the lightly armed scouting foray moving ahead of the main force.

There's plenty of challenge, since each class has a separately programmed AI, so they can make the most of what they have and the level bonuses give them more to work with. E.g. if you play a Warlock against an Emperor Warlock, on your starting gem income you can make your first summon on turn 10. The Emperor AI will be making its first summon on turn 2. The power difference starts diverging fast...