U7 was the best of the series, and drew me in like no other RPG before or since.
IMHO, it is a MUST PLAY… You won't regret it!
U7 is more of an anti-RPG, what one might call the first meta-RPG. The combat is atrocious, the inventory system is unbearable and it requires more pre-knowledge of the genre to fully appreciate than probably any other RPG other than something like Undertale.
As such it holds a special place in the pantheon of RPGs, just like Plansescape: Torment does, and just like Underale does, but the extent to which it's a must-play will depend heavily on your desire to experience something that prefers mocking RPG conventions than providing a good example of the conventions.
And you'll notice a theme here with these kind of games, the anti-RPGs, yes, they don't tend to have sequels and copy-cats. Because if they did then they'd become their own conventions, which destroys the whole point of making something purely meta and mocking.
In terms of why some people really like it beyond the joke of joking, it's probably the most adventure game/sim version of an RPG you can buy, so if you like obtuse puzzles combined with excessive backtracking to specific NPC quest-givers with as little bother from combat as possible and you like the idea of that NPC possibly not being there because they've gone to bed or fancied a walk in the fields then, sure, this game is entirely your bag.
I liked the graphics a lot, I have a very big soft spot for the lovely bright and colourful isometric designs of the early 1990s, of which Heroes of Might and Magic 1 and 2 are probably the pinacle, so for me it angered me greatly that the game didn't provide the same quality of combat gameplay that those wonderful graphics deserved.
In terms of main quest, it's one of those games where you have to get a thing, to get a thing, to get a thing, to get a thing, to get a thing, to get a thing, like most of the really obtuse adventure games. In terms of sidequests it's a bit more fun, but the constant backtracking soon drains the enthusiasm there.
The things it brought to the table for future cRPGs are all those sim-obsession things like day and night cycles, NPC schedules, the joy of baking bread for the sake of baking bread, possibly the first game with genuinely interesting and unique companions with their own agendas etc etc, but all that stuff has never really mattered to me while some people seem to think all these distractions are the
only thing that matters, so I do have a very strong personal bias against it historically, even though I did give it a fair shot of a good 20-30 hours, much more than I would any other game I'm not enjoying.
In terms of whether it's a 'must play' I'd have to disagree. Meta-games are usually very much stuck in the memes and conventions of their time even more so than regular games of the same era and this game is no exception. If you've already played a lot of games from that era and need some comedy light relief of the conventions of that era, but for some reason haven't played this yet, then, sure, it's probably got something to offer, but as your first or second delve into that era, then, no, you're not going to be getting most of it's point & you'll just be frustrated by the appalling gameplay and UI.
The only reason I'd recommend this game to a 90s era newcomer would be if they had a specific thing for meta-RPGs generally, like if they only really liked Undertale or Plansescape: Torment out of either the 2000s era or modern era respectively.