Combine hack & slash gaming with a realtime RPG and you've got Crossfire. You've got the D&D stats, its common races and classes, spells/prayers and all your usual magical items. Gods can be worshipped and they grant powers, even if you are not a priest. There is also a skills system to gain levels in. You can play solo or team up with people you meet to form a party, taking on harder and harder monsters, discovering more and more about the world.
I first played crossfire around 1994 on a Sun workstation at the university. It was an awesome game at the time. About as good as the arcade game, Gauntlet, it was inspired from, but multiplayer! With lots of extras. I've come back to the game now and then over the years and still like it.
Over the years since then it has had its ups and downs in the development pace. Much of it is still the same, just improved and refined, but of course many entirely new features have been added as well.
From a graphics point of view the game can't compare with modern games. The graphics is simple, top view 2D and it does not aim to be photorealistic in any way. Like many games of its time, you move from tile to tile, there is no per pixel movement at all. The lighting is per tile (even though clients smooth between them). However once you start playing you realize that doesn't matter at all.Its loads of fun walking through hoards of goblins like mowing a lawn.
There are now thousands of maps to explore, hundreds of different monsters to learn about. Lots of races, classes and gods to combine together with loads of different armour and magical items making you into a powerful, but unique character. You can even create your own weapons and armour.
There is a quest system and the system supports building advanced puzzles, but neither is yet used to its full potential. Puzzles tend to be of the hack & slash or exploration/discovery kind more than having to think hard. Find the switch, avoid the trap, kill the boss. Sometimes talking with the right NPC to get the password or finding the right item some other NPC needs.
The reason I don't give crossfire a five is that it is developed as a truly free software project. Free software is great for building game engines and tools, but not so great for art like games. Like most free software projects, people work on what scratches their itch. Adding cool features, designing their map etc. The technology is solid (given the tile based design), with lots and lots of features, but there is not a singular artistic vision. Its more consensus and lots of choices you can make when compiling the server, which even though crossfire is unique also makes it a bit bland. The crossfire distribution of maps, sounds and arches (the tile building blocks) can be played as it is, but it is really meant to be used as a basis for your own game. There are a few long running servers around where they have done that.