I was speaking to a friend who recommended I do so. But I was looking for some extra opinions.
My experiences with the 1st 3 generations of pokemon gave me the opinion that pokemon wasn't really a plot heavy game (though lore/trivia can be surprisingly deep). The games are generally formulaic (gotta catch 'em all, 8 badges, a rival who usually takes a starter super effective against yours, a criminal organisation to wreck, an elite 4 and a champion to beat) Only big surprise I can recall with nostalgia googles in full effect is gen 2's double region. From what I vaguely recall reading SuMo was surprisingly plot heavy apparently.
My original plan was to just play Ultra SuMo as a remaster. Some of what I've read said I won't lose out on much by just playing Ultra, besides neatly seeing subversions of what happens in SuMo/the rest of the series? (One that I'm not sure might have been is rival picking a starter weak to mine).
Best Answer
The plot of Ultra Sun and Ultra Moon is an alternate retelling of the plot of Sun and Moon. It is not a sequel like Black 2 and White 2 were to Black and White, so it can be fully enjoyed without having any knowledge of Sun and Moon.
In fact, I'd go as far as to say that since Sun and Moon have a very unfinished feeling to them, it is probably better to not play them before Ultra Sun and Ultra Moon.