My only dependency is SDL2; I treat it as my "platform", so it handles windowing, input and audio. This means my Cargo.toml is as simple as:
[dependencies.sdl2] version = "0.35" default-features = false features = ["mixer"]
this pulls around 6-7 other dependencies.
I am doing actual true color 3D rendering (with Z buffer, transforming, lighting and rasterizing each triangle and so on, no special techniques or raycasting), the framebuffer is 320x180 (widescreen 320x240). SDL handles the hardware-accelerated final scaling to the display resolution (if available, for example in VMs it's sometimes not so it's pure software). I do my own physics, quaternion/matrix/vector math, TGA and OBJ loading.
Performance: I have not spent a lot of time on this really, but I am kind of satisfied: FPS ranges from [200-500] on a 2011 i5 Thinkpad to [70-80] on a 2005 Pentium laptop (this could barely run rustc...I had to jump through some hoops to make it work on 32 bit Linux), to [40-50] on a RaspberryPi 3B+. I don't have more modern hardware to test.
All of this is single threaded, no SIMD, no inline asm. Also, implementing interlaced rendering provided a +50% perf boost (and a nice effect).
The Pentium laptop has an ATI (yes) chip which is, maybe not surprisingly, supported perfectly by SDL.
Regarding Rust: I've barely touched the language. I am using it more as a "C with vec!s, borrow checker, pattern matching, error propagation, and traits". I love the syntax of the subset that I use; it's crystal clear, readable, ergonomic. Things like matches/ifs returning values are extremely useful for concise and productive code. However, pro/idiomatic code that I see around, looks unreadable to me. I've written all of the code from scratch on my own terms, so this was not a problem, but still... In any case, the ecosystem and tooling are amazing. All in all, an amazing development experience. I am a bit afraid to switch back to C++ for my next project.
Also, rustup/cargo made things a walk in the park while creating a deployment script that automates the whole process: after a commit, it scans source files for used assets and packages only those, copies dependencies (DLLs for Win), sets up build dependencies depending on the target, builds all 3 targets (Win10_64, Linux32, Linux64), bundles everything into separate zips and uploads them to my local server. I am doing this from a 64bit Lubuntu 18.04 virtual machine.
You can try the game and read all info about it on the linked itch.io page: https://totenarctanz.itch.io/a-scavenging-trip
All assets (audio/images/fonts) where also made by me for this project (you could guess from the low quality).
Development tools: Geany (on Linux), notepad++ (on Windows), both vanilla with no plugins, Blender, Gimp, REAPER.
I've become too familiar with it over testing to notice unintuitive behaviour, but I think I understand what feels off: in real world units, the gradual region you describe is very wide, and feels linear. This would make for very boring gameplay (imagine spending minutes to reach the planet). You need to keep the playable area [radiusForce0, radiusForceMax] small. So you will either map that small [r0, rmax] into real world [F0, Fmax], which means the force will be almost constant across, or "compress" the [F0, Fmax] curve so that you can fit both [zero outer space gravity, strong surface gravity] into that [r0, rmax].
That's what happens here, I probably tweaked the values for the second case. It's kind of an accelerated version of reality and the margins feel very tight, and you have to "buy into" that reality.
For example, Master difficulty in Mission 1 may seem impossible, but if you try to be gentle and find a balanced orbit, you can complete it with miniscule fluctuations in distance and minimal input.
Just rambling though, I never really actually designed or balanced the game.
the unintuitive behavior is that it is very difficult to find that balance. if i am to slow i crash into the planet, if i am to fast i leave orbit with no chance to get back in time. being gentle always results in being to slow. in other words there is no gentle way to reach the balance. and if i don't know where that balance is, i don't know what to aim for.
you may argue that finding that balance is the goal of the game, but then i guess the game is not for me. i lose interest if i have to try 10 times and still can't figure out how to do it right.
There are some methods that help a lot, like keeping a completely perpendicular or parallel viewing direction, and adjusting the distance with the corresponding set of thrusters. Even slight angles mean you have to randomly mash forward/backward/left/right and hope to keep a steady orbit, it's not gonna happen.
For what it's worth, even for me now, it would take more than 10 tries probably to beat Master on Mission 1.