"Gothic" is, along with "Two Worlds" and "Oblivion", one of my all-time favourite action role-playing games. What enthralls me most in the genre is a beautiful, detailed, large, and believable world. "Gothic" has one of the most interesting ones and has been designed with a lot of care. It tends a lot to relatively worn-out clichés, but it is all so well done that one can't really care. That you can watch your co-inhabitants get up yawning in the morning, going around their daily business, and enjoying a meal and some music around the campfire in the evening adds a lot to how realistic the world around you feels. To shallow players, things like that might seem unnecessary coating, but it is what, for instance, earned Origin the title of "world creators". Piranha Bytes achieved this as well with their Gothic series - a fantasy world that you always like to revisit, not just to complete the storyline and the game, but because it is nice to look at, there's always something to discover, and you got to know it so well over the course of the game to the point that it feels a little like a virtual home away from home.
The beautiful soundtrack, the interesting characters and the fitting voice acting do their part to support the atmosphere and immersiveness. What keeps you playing is the raw standard action-RPG gameplay: a constantly evolving character that rises from zero to hero, a lot of loot to pick up and a lot of money to spend. It's nothing new or special, but it has everything that can make this kind of game so addictive.
The downsides of the game don't really weigh much against all its strengths. The controls have been widely criticised, and rightly so. The weird key combinations and mouse movements you have to perform to interact with the world might feel a bit strange for the first couple of minutes. You get used to it of course, but it's an unnecessary barrier. I don't think there's many people like that on GOG, but if you lose your motivation with a game if you can't completely master it in the first 3 minutes, this might be a problem. Also, the storyline really loses all of its personality towards the end, and drowns in a sea of mediocrity. But by then you will most likely have fallen so much in love with this game that you'll instantly go on to play its sequel, which will make you quickly forget about the subpar finale of the first title.
If you have any interest at all in action-oriented, real-time CRPGs, if you enjoyed the likes of Two Worlds or The Elder Scrolls series, this is a game that you will heartily enjoy and remember for a long time.