You mentioned so many important things in this post so I can't comment on them all.
Game mechanic and rules influence how you play. There are game systems like D&D where a group can work with a player who had a bad day or who normally doesn't participate much aside from rolling the dice when needed. Others, like FATE, need constant participation because you have to think more about the "how" to deal with situations in the game.
Additionally to changing systems you can change being the GM. GMing is fun, but playing is fun too ;) We do that in my "The dark eye"-group. I'm looking forward to playing when I'm the GM and vice versa.
The differences between games is something that I don't think people can ever state enough.
People often approach tabletop roleplaying as something where you've got this sort of universal act of roleplaying, and the game is just a facilitator.
In a sense, that's true, because a lot of the social dynamic is almost universal and the way you play will typically be the same.
However, there are so many variables that change that you can't really predict what you'll enjoy and what you won't. I remember getting a little burnt out when I first ran Shadowrun, but I look back on it very fondly because the only real reason for that was that I had eight players (with a peak of seven at any given session) in the first game I ever ran. That's a bit many.
The Dark Eye is on my roleplaying bucket list. Back in the day I got an older edition of the rules off of DriveThruRPG (I believe it was translated and distributed in the US by FanPro), but it wasn't quite a full edition like you would really want. There are a handful of other games (Symbaroum, Earthdawn, Fading Suns, Heavy Gear/Mekton Zeta, the Battletech RPGs, Legend of the Five Rings) that I'd really love to play sometime.