The first two Gothic games are without any doubt more refined than Risen storywise.

I like them for their ambiente, their lack of "epicness", gameplay and living world.

I think it's fair to say that you don't have any decission in the overall story til the 3rd game. It's compareablebe to Risen, the decission mostly mean, choosing different ways to achiev one general goal and mostly affect the relationships to NPCs. You know Bandit, Inquisiton, Mage for the story it doesn't matter but some NPCs react differently according to your choice and you have to/can different quests.
Gothic 1 & 2 is the same. I dare say both are better how much your decissions affect afore mentioned stuff.

The overall story isn't childish but it's also not really original.(The setting of Gothic 1 is original and a masterpiece) Most fans of the series would probably tell that it isn't about the story rather the... hmmm how to put it... the stuff you do in the first chapter of Risen. Trying to fit in, explore the world, the people...

Do i care for the charakters, yes i do. There isn't really any character development(and especially inth the 3rd game there are terrible inconsistencies) but you probably will become attatched to some.

Actually the "real story" only unfolds in the 3rd game. By real i mean the whys are finnally lifted... no not really, the 3rd game is horrible storytelling wise(It's closer to TES than to Gothic or Risen). Still it explains whats behind some stuff.
Anyways for the most part it's kind of kill some antagonist and that's it. Sounds like typical good vs evil? More or less at rare occations it's more than that but for the most part you don't ask long quetions(lack of epicness) someones beeing "evil" kill him.
Again this is just for the main story. Most NPCs aren't evil or good(though they may be douchebags ;)).

Bottom line, yes they are like Risen. :)