It's really hard to compare the two, the gulf of differences is so vast.
BG III has much higher production values-and it shows in many ways where it stands head and shoulders above its predecessor, but in others it feels weirdly unpolished and janky. But fundamentally-quality aside, they seem to me like very different games to me. The Pathfinder games are more comparable to BG II than BGIII. BG III feels more like a fusion of DOS2 and NWN2, honestly.
Now do I like BG III more than BG II? It's a difficult question to approach given the above, but I'd have to say....no....and a large part of that just comes down to the foundation of the game, only tangentially related to anything Larian is doing.
BG II was written when 2e was transitioning to 3e-what I have heard many (I'm one of them) folk describe as the 'golden era' of the Forgotten Realms as a setting. BG III is set in the Post-Spellplague era, when WoTC treats the lore of its settings as essentially disposable, where retcons and the advancing timeline have rendered the setting recognizable only on a surface level. Obviously I prefer the former, but I think that even those that prefer the latter would admit that the Forgotten Realms of the old games is a different animal. I have a great amount of nostalgia for this era of the Forgotten Realms, and BG II is a huge part of that.
Now for Larian's part, they are-under their own admission- leveraging that nostalgia. IIRC Swen himself admitted the big reason why they were making a BG sequel in the setting instead of an unrelated game was the name recognition/nostalgia factor. But IMHO Larian was already starting at a mandatory handicap by having to use the inferior 5e iteration of the setting (YMMV), and they have shown several times in EA that they are willing to play fast and loose with the already shaky 5e setting & lore. Since I'm playing this game in no small part because of my love of a setting that cannot and will not be replicated in BG III, I don't think the nostalgia/fanservice/etc hits the same way as intended. If anything, it makes me feel slightly apprehensive and uncomfortable.
There's also the question of if a sequel ever really needed to be made. The original (cancelled) BG III was going to feature a new protagonist and unconnected story because the story of the original saga was considered 'done', but fast-forward to today and we have 'Murder in Baldur's Gate' which brought back Bhaal- a fundamental piece of background for the setting of BG III, since we know Bhaal is going to be a major part of the plot. In doing so, MIBG invalidated the choices of the players of the original saga, both in the ultimate sense (because Bhaal came back and the Bhaalspawn is dead), and by robbing players of the agency to even imagine their own Bhaalspawn in bringing back Abdel Adrian, the infamous protagonist of the novelizations-making him the canon protagonist before killing him off out of hand at the end of it all. The legacy of the protagonist of the old saga is pathetic and forgettable and overshadowed by their companions. I don't know how Larian intends to address that in a game that's a sequel without double underlining the unfortunate legacy (or lack thereof) of the original BG protagonist.
This is aside from the general qualities of BG III itself, which have both its ups and its downs in regard to the original saga IMO.
