This is a great simulator for the space nerds like myself who can overlook some of its rough edges - the more you know about the Mercury missions the sim depicts, the more enjoyment you'll get out of it. It's the work of a solo developer, so a certain level of polish is understandably lacking, but it gets enough right that it is definitely worth experiencing.
I don't have a VR headset, so this is solely from the perspective of someone playing it with a desktop setup. There's no way that I've found to change the controls or use a joystick, so you have to make do with the keyboard controls. This isn't a space sandbox like KSP - it's a hardcore systems simulation following the exact flight trajectories of the Mercury missions. Just like the real astronauts, your control is limited to the reaction control system for orientation, and that's about it. Abbreviated checklists are provided with an optional "helper" function which highlights the next step, and although sometimes the checklists can be buggy, the mission almost always continues as long as you've checked the most important steps. The countdowns and preflights are also abbreviated but still long (circa 10 minutes which is mostly waiting), although there is an option to speed up time which thankfully returns to 1x speed whenever important voice lines start. Almost all of the important switches and gauges are fully functional and you can see the impact of flipping an incorrect switch in real-time. A few options are missing, like the ability to change the filters or magnification of the periscope, red filters for the cockpit lights, etc, but these are minor omissions that speak to the level of detail the sim already exhibits.
One thing that can't go unmentioned is the glorious sound design. This sim would be nothing without it. The missions are synced up to the actual mission audio from the astronauts and the various control centers, and as long as you're not screwing around, they're accurate down to a few seconds. Hearing the astronauts joking with each other and getting through stressful moments creates an INCREDIBLE level of immersion. Due to the real-life astronauts' rigorous reporting procedures, you can follow along with their exact actions and procedures. A highlight for me was after splashdown of MR-4 where Gus Grissom reads out every switch and gauge condition and you can truly appreciate the accuracy of the cockpit. Unfortunately this does tend to highlight the sometimes-inaccurate gauge readings, and those which are non-functional like the descent speed indicator, but for the most part it's a thrill to follow along as Alan Shepard checks the pitch, yaw, and roll axes of Freedom 7 and imagine what it must have been like. Electrical hums, fans, and switch clicks are dead on. The ignitions are very loud and engine noise gradually grows quieter as you leave the atmosphere. On lift-off and re-entry you can hear the panels vibrating and bumping into each other. In my opinion, sound is one of the most important elements of immersive sims and this is superb.
The first four Mercury missions are modeled in their entirety. The ~5 hour Mercury Atlas missions include both the realistic 3 orbit and an abbreviated 1 orbit variation. It clearly seems designed for the 1 orbit version, since there's no mission audio during the latter two orbits - it would be nice if those audio logs were included for the longer flights. No 35-hour-long, 22 orbit Faith 7 mission either, rats! There isn't a lot of "gameplay" here. Just like the real pilots, you're mostly along for the ride. The astronauts were also busy conducting experiments, taking photos, and recording anthropometric data which we don't get to do in the sim, and their workload was very high trying to cram as much science into these short hops as possible. These tasks may not seem fun to many, but for VR and immersion I can imagine they would make a big difference - taking photos out of the window at a certain stage of the orbit, for instance.
Some people like to find the limits of simulations by doing deliberately unrealistic things, and here there's nothing you can really do to get a bad outcome - you can mess up badly, but you'll never die or crash. As a test I did everything wrong - fired the retro rockets in an incorrect orientation, went nose-first into re-entry (the capsule rights itself), and shut down all the electrical systems but both chutes and the landing bag still deployed safely. You can't die from overheating, depressurizing the cabin, or depowering. But that's not really what the sim is about - as a Mercury simulator it's more about replicating how the missions actually transpired rather than experimenting with what could have gone wrong. Even if it didn't affect the outcome, I was still realistically micromanaging the systems and juggling suit cooling with cabin humidity when I flew MA-6 because I wanted to experience the real challenges NASA faced. As long as you stay within the confines of common sense, the illusion of the simulation is excellent.
Hopefully that gives a clear picture of what this sim offers. It still needs work, it's definitely not for everyone, but if you love the history of the space race and systems/flight simulation, it's a welcome break from the fantasy options that are available and in my opinion is unmatched for immersion. If you're still unsure, the game has an excellent demo which will give you a good idea of whether or not this sim is for you.
