Help me out people. I like story-heavy games but I never tried VNs. Can anyone recommend me a good entry point for VNs, most preferably with an adult cast and maybe darker themes?
Ace Attorney is my go to recommendation. Not too long, inexpensive to own the first trilogy, and some enjoyable courtroom/investigation to break up the constant barrage of text for people not used to the medium. Hits really well on both the comedic scenes and some heavy moments. There's also stuff like AI: The Somnium Files, and the Zero Escape Trilogy (999, VLR, ZTD) as well for good entry points. The Utawarerumono trilogy is also fantastic with the 3rd game being a personal favorite of mine (and one of the only pieces of media to make me cry).
If you have a PS4 look into Aegis Rim: 13 Sentinels, which is an iincredibly out there scfi-fi epic while simultaneously being a really fucking amazing visual novel/RTS hybrid.
Someone also mentioned The Sekimeiya: Spun Glass, which I haven't gotten around to reading yet, but sounds fantastic and might be something that you're probably looking for.
While I'm not a personal fan, Fata Morgana is one of the most highly rated VNs for good reason. It's incredibly dark and at times, really hard to stomach, but there's very little quite like it in this medium.
The science adventure novels like Steins;Gate, Chaos;Head Noah, Chaos;Child, and Robotics;Notes are all also great VNs. I haven't gotten to reading them yet since I'm waiting for Chaos;Head Noah's fantl to finish before i binge the series, but I know many who can speak to their quality. If you do look into picking these up, look into the committee of zero fan patches for the Steam versions of these games. They fix a lot of the translation errors and spelling that exists since outside of S;G these titles unfortunately got pretty middling translations.
I'd recommend staying away from the nearly 100+ hour juggernauts like Baldr Sky, Muv-Luv, Muramasa, Dies Irae, Higurashi/Umineko, etc. for your first go around. Not that they're lacking in quality, as even with my personal gripes with some of these titles more than others, they all stand as some of the highest points of the medium. But they can be tough for newer players thanks to their occasionally erratic pacing or difficult writing styles (and sometimes even a combination of both). VNs like those are best read once you're more accustomed to what to expect from the medium.
One thing to keep in mind is that visual novels is a really wide and expansive medium of entertainment, similar to anime/managa/tv/etc. Even if you don't jive with everything, there's always something out there for everyone considering the wide number of genres they touch upon.
There's also a genre called Nukige or "Crying Game" which is aimed at sad stories or stories to make you feel things which would tend towards more mature/adult themes like loss etc.
You're thinking of Nakige, Nukige is uh....something much different involving adult themes.