Story could be better, "evilness" is a gimmick, gameplay is great, boss fights are a joke: Lacks substance.
Story:
When you begin a new game, an animation shows your minions (creatures you're able to control to kill, loot, die for you later on) have dug under dirt and rock to find your body. You're then being dressed in armor and you're then called the "Overlord", the new ruler of Evil. Afterward you're instructed to rebuild your tower and throne, by a generic evil version of Star Wars' Yoda.
From here you're pillaging loot, killing random creatures and people, while taking up a few new quests as you visit each area. These quests are poorly written, as is the main story line itself.
Graphics:
They're good, but not great nor bad. They do the job.
However, the artistic style of maps is odd and questionable due to how one area of the map is merged with the other.
Some areas are very nice though.
The graphics for the main character when moving can feel as if you're lagging, jagged movement. I'm not sure if it's a programming error or animation error however.
Sound:
Extremely generic. In fact, some of it sounds as if it were copy & pasted from Age of Empires 2. For example the lumber jacks in Age of Empires 2, cut down a tree, that sound would then be used in Overlord for maybe killing a tree monster or breaking a wooden gate. Believe it or not, but the same sound for breaking a wooden gate was also used for a boss monster!
Gameplay:
Nothing special, does the job. Controls are fine, but can sometimes glitch. For example if you left click to send your minions to attack, click left click too much and the game then puts your minions into sweep mode and you end up having to press right click or right+left click same time to disengage this. A minor issue.
What were the main features are gimmicks:
The minions were supposed to be humorous, but they're far from it. Maybe their voice acting and lame "jokes" could entertain an 8 year old, but an early teen and older would yawn or pull weird faces.
The evilness is a joke, not a good one nor will it literally make you laugh. More of the sarcastic type, the "What the * is this? You're kidding me...".
Your evilness is limited and isn't even worth trying to gain 100% evil ranking in game, as it's a waste of time, doesn't effect much in gameplay at all.
Summary:
The story lacks a lot of substance, is lost and very puzzling. The game is illogical and leaves you to basically quest to your hearts content through randomness, visiting new areas and completing some puzzles along the way.
This game is nothing more than a bargain buy for the PC, a rent for consoles, for nothing more than maybe some pure fun for your boredom.