About menus and GUI scale, aren't it are standard for the time? Since games meant to be played at 640x480 or 800x600 anyway nobody seen a problem with that. I think vanilla quake 2 does it too. And some other games had even more wierdly implemented menus.
Maybe they have the Barney Miller remake on streaming services in the 2030s?
Also, SIN source port does not exist? Since idtech2 is opensource for a very long time and I don't remember when I played the original Quake 2 last time on modern hardware.
However, in many ways Sin looked more advanced in plot and mechanics than more later Raven's Soldier of Fortune from 2000. SoF shows more shortcomings of the Q2 engine and does not have stuff like helicopter turret sections and felt much less alive. Raven did a much better job on their idtech3 engine games.
Bonus points for Quake 2 "jelly models" because 8bit per vertex coordinate limitation! Quake 2 also had no skeleton animation support of course and IIRC and animation interpolation worked weird. Also, the texture depth buffer on the non-map object had limitations. Lack of draw distance detail is the result of Sin using a lot of external 3d objects instead of map brushes which was not really common back then for such games, like in half-life and quake everything, even stuff like trucks is map brushes. I suspect that this is also the result of weird lights on soda cans from cutscene: they are an external 3d model, not a map object so lights do not affect them. I think, only old Bethesda in the 90s heavily used such stuff to construct entire levels.
Lips animation in general not something common in-game before... 2000? And sin cutscenes were in-game ones mostly, not recorded movie files on a CD. Yea there was Half-Life, but still. And I think making lips animations by animated texture like you showed was kind of a pain in the ass, I remember such technique used in-game on idtech3 Raven's Star Trek Voyager Elite Force. Drakan Order of the Flame has no them, so TES Adventures Redguard that came out the same time as HL1 and Sin outside pre-rendered cinematics.