I would agree with an arbitrary watershed at pre-1990 and post-1990, though I'm sure it's not actually a sharp boundary.
With 'old' SF what jars is sexism; the portrayal of women as sex-bombs and airheads, and of men as driven by power struggles and genitals. I don't mind quaint technology so much but I do mind that most encounters with aliens almost invariably have the aliens as dangerous, out to kill, subjugate or eat us, or steal or transform our planet. Of course there are many terrific stories and series from this era too. The best possible combo, from my PoV, is an older novel with strong, independent female characters, and this is one of the reasons I like the work of CJ Cherryh and Octavia Butler so much.
With 'new' SF most of these negatives have disappeared. Stories have become more complex and nuanced, often with philosophical and ethical overtones. It is terrific to see women depicted as captains, scientists, heads of teams - all functioning competently & autonomously without men to do the heavy stuff and rescue the gals when inevitably they fall apart. Some of the most modern work (and I confess I haven't read a lot of it) does have a kind of 'yoofspeak' that I find distracting.