Whether singleplayer or with a group of friends, the old classic action rpg "Sacred Gold" is still lots of fun to play and still one of the best games of its genre.
A huge vivid open world with lots of secrets to discover encourages traveling around and exploring, the character development is highly customizable with Combat Arts, self-selected Skills and Attributes. Apart from usual randomly generated loot, there are uniques and set items which encourages collecting, and equipment in general has so many different possible modifiers that you can highly customize your character in so many different ways.
There are five difficulties, you unlock the next higher one by beating the game on the previous. Each difficulty makes enemies deal a lot more damage and become tougher, but also improves the loot you can get from them. The game gets extremely hard on the highest difficulties.
I don't have this game in Steam for long, played it many houndreds of hours before (probably far more than 1000 hours over the years, actually), it's just awesome.
I'd say it's even worth the standard 10€ price but this is debatable, at a sale though I can only fully recommend it.