Generally speaking, taking the train in France is a rather good experience. The trains are quiet and confortable, especially the high-speed ones but even regular trains are fine. Newer carriages have power outlets at the seats and are well ventilated.
The issues people here fear the most are strikes (which is the national sport, particularly in public transportation) and the creeping-up of prices, especially now that there won't be any more competition from planes.
To the OP complaining about Sweden, I actually don't find the train service in Sweden so bad. Sure it's not on the same level as France and Germany, but the trip between Stockholm and Gothenburg is still fast enough even discounting the added time of getting into the center, parking etc. you have 3h for the train vs 5h by car. And the cost is ~30 euros. I also find the complaint about motion sickness funny, compared to planes and cars the Swedish trains are still very smooth.
The more rapid but shorter lateral movements on a plane does not trigger my motion sickness, and neither do turbulence. That could be a personal aspect. I have the same issue where if I am on a boat that goes up and down then I am usually fine, but not if the waves comes side to side.
You might have seen those. Bright color, « futuristic » design. In the vein of the concord Suprasonic plane.
The German rail system has also been detoriating in the last decades due to lack of investment of the Deutsche Bahn after being privatized. You don't see it on the main lines, but you see it on the lesser used ones.
The rail system has been stagnated in the last 40-50 years and maintenance neglected. The rail is not straight and gives a lot of lateral movement, vibration and noise. The train departments are not sound isolated or have air condition. The speed limit (as a result of the neglect) makes the trip slower than on the highway, with around 30m in favor of the car on a 3hr trip. Motion sickness is an obvious problem. Because of the lack of maintenance, there is almost never alternative rail tracks which mean that when they do maintenance they have to shutdown the whole track and switch to bus, often doubling or tripling the total traveling time. Train tickets is also about 100-200% the cost for distances above 3hrs.
I don't know if the French rail is better, through I do know the German one is. Getting into a train department with sound isolation, air condition, plenty of space and almost zero lateral movement was amazing (sample size of one trip I made between two large city centers), and if that was the option I would pick that ever time even if the train was slower or costed more. It is the 50 years old black tin can of motion sickness that makes me pick a plane over a train.