Gave it a go and completed Medical (3/3/3/3 difficulty). I was skeptical at first, because I thought the source port's renderer made everything look kinda flat, and I actually don't think it's a very good idea to streamline the controls much more than the Enhanced Edition already does. But, it's nice to have a source port with more configuration options, especially higher resolution support. It also seems that there might be some kind of midi emulation built in, since many of the music-related issues present in e.g. radiation zones and cyberspace sections are gone, and there seems to be a new standard soundfont.
As for the visuals, I was able to more or less recreate the old "denser" look of the game by toggling the DOS shade table instead of the new shade table. See my video options below. Everything is default except for the shade table, detail (software) set to Min (honestly not sure what this does), and anti-aliasing enabled.
You can compare the DOS and new shade table below. The new one is obviously "better" in that it's softer and more subtle, but I frankly prefer the harsh contrast of the DOS shade table.
I also can't figure out how to disable the "optional" Mac textures, as I honestly like the look of DOS SHODAN better and would like it back. Comparison:
A quick note on gameplay: I think it's a bad idea to use many of the hotkeys they've made available to you, such as reload/healing patch/grenade/quick pickup hotkeys. SS1's combat is already rather straightforward with the mouselook mod, and much of the tension and challenge that was still there came from managing so many things manually in the interface in the midst of danger. Since reloading is instant save for the time it takes to mouse over from your target to the reload button, a reload hotkey renders magazine capacities as essentially pointless. Also notable is that there used to be a functional difference between dry reloads and tactical reloads, since you had to click once to unload a partially unspent magazine and again to load the desired ammunition type -- a reload hotkey merges these functions and removes another element that you had to keep track of. Other hotkeys streamline gameplay in a similar manner, to the detriment of tense moments where you're cornered and have to improvise a way to get out of a sticky situation. I appreciate that you can rebind hotkeys for your implants and whatnot, but I think it might have been best if they had left out many of the new ones.
To clarify, I don't think streamlining the interface from e.g. SS1 to SS2 was a bad thing -- I'd argue that Deus Ex/Thief/SS2/Arx Fatalis perfected the interaction paradigm in this sort of game with minimal loss of depth. Nor am I one of those people who insists you must play Doom with arrowlook, alt-strafe and CTRL to fire; or even SS1 without the mouselook mod for that matter. But the difference is that those convenience/quality of life features don't delegitimize entire chunks of gameplay. Doom still has tough encounter design that requires careful movement, weapon selection, and target prioritization with mouselook, and SS2 importantly compensated for its greater fluidity in gameplay and refined interface with aggressive enemies which did more than slowly shamble at you like turrets with legs. With the need to juggle the interface removed alongside the more straightforward movement and aiming from the mouselook mod, the flaws of SS1's combat design are stretched to a breaking point. It's like replacing Resident Evil 1's tank controls with Hotline Miami's topdown setup and expecting any of the horror or dread to remain in the absence of any other changes to AI, weapon design, and so on.
Generally speaking, the source port is definitely an upgrade just for some of the configuration options, bugfixes, and technical improvements, but you should be careful how you use it if you want to experience System Shock 1 without ruining it for yourself.
One last thing; I didn't see any way to opt out of the source port. I previously had SS1 installed from Steam, and assumed I'd get some option when I launched the game. Instead, it just downloaded the update and I no longer seem to have the
DOSbox version old Windows port at all, nor do I have any of my old saves. Not a huge deal since I wasn't in the middle of a playthrough or anything, but I feel like this could have been handled more transparently. Back up your SS1EE folders if you want to keep your old stuff, I guess.