I'm going to ramble and meander between points and I don't care enough to further cajole this into greater coherence, but my thoughts on Pillars as a series:
Pillars 1 was a lengthy game that didn't do a great job of hooking the player beyond "we are making an infinity Engine spiritual successor". Fact is, these guys were, at least in part, the guys that made Icewind Dale, not Baldurs Gate, and it shows. I know many codexers love full party creation as seen in IW, but it turns a lot of people off and I think on some level, the legacy of Icewind Dale passed into Pillars. The companions were not great, some were ok, but there are no real standouts that come to mind.
A thought I often had in mind regarding BioWare vs Obsidian characters (at least during the New Vegas>Pillars 1 era) was that BioWare created memorable characters, while by contrast Obsidian created starkly realistic characters. How that breaks down is, yes you may well be taking on a counsellor role in a BioWare game in terms of solving their Daddy issues or whatnot, but you were at least left with a character that stuck in your mind. Obsidian by contrast I always described as written well/realistically enough that they would/could solve their own problems by and large without needing my character's intervention. I'll always remember Viconia, Morrigan, Minsc, Sarevok, etc because they stick in my mind, even if that's largely because of their larger-than-life personalities. Another way I'd describe it would be that Bio's (pre-DA2 at least) characters are people that I would want to go on adventure with (from a fun/enjoyment perspective), whereas Obsidian's offerings would do fine on their own without my character's input. Essentially, one provides fun and enjoyment while I'm out questing, while the other... doesn't.
I'm not going to single any one person or thing out, but Pillars 1 had pacing issues and was in large part quite boring. I will note that using IE Mod to disable the gold backer npc interactions did improve the pacing on my 2nd, unfinished run through the game, but that's a whole bunch of superfluous dialogue that had no place being there to begin with. It made environments a chore to explore in much the same way Shadowrun Hong Kong faltered (Torment Tides being a recent extreme example of the same thing).
When it was first announced, Pillars 2 wasn't off to a strong start for me. On the face of it, its setting immediately made me recall Suikoden IV, the black sheep of that series. Sailing around a huge ocean visiting islands held about as much appeal as trekking through a desert to me. The "oh now you're a pirate, lol" thing just seemed slapped in there to justify this new approach as well. That said, when Pillars 2 got rolling, I ended up enjoying it a lot, plus, critically, I actually started caring about both my own Watcher and their companions fairly soon into PoE2, this wasn't the case with the first game so the second game was definitely doing something right. I enjoyed adventuring with most of the companions in PoE2 though the story progression was bizarrely segmented with how Eothas was handled. I'd probably have preferred them ditching the ship & open sailing entirely and doing something like Geneforge 3 did where you do all the quests on island 1, then you chase Eothas to island 2 (no backtracking permitted), and so on. This would have cut out a lot of the garbage bounty filler content they stuffed into the game as well. The sequences with the Gods and meetings with Eothas were also enjoyable, I just feel it would have been better as a somewhat more linear experience, I don't feel the sailing did anything except pad the game length and fracture the plot/pacing. DLC content also benefits from the tighter focus.
There's people in my friends list on Steam with Pillars 2 in their library, who won't jump into it as they never finished Pillars 1, a game they stopped playing presumably because it didn't hold their interest until the end of the game. When I think of Pillars 1, I think of a game with a lot of dry dialogue, frequent lengthy forays into the nuances of Dyrwoodan politics and a veritable army of backer npcs cluttering the streets with "click me!" signs over their heads just waiting to deliver a diatribe of irrelevant nonsense (poorly aping say the dream sequences in say Lost Oddysey, which were used sparingly and thus retained their narrative impact). In some ways PoE1 stands as a monolithic wall barring entry to a superior sequel.
Contrasted with the Baldurs Gate 1>2 transition which the overarching Bhaal story and Sarevok/Irenicus as primary antagonists, Pillars1>2's story around the Watcher wasn't immediately compelling; the Thaos setup didn't drive me along through the game like the revenge motivator did with Sarevok. Any personal motivators in the Pillars 1 plot fell flat for me, though I did like the world setup, especially with regards to souls.
I'll underline here, for any sequel where the previous game hasn't fully wrapped up a given overarching story, I would much rather play as a returning protagonist and I did genuinely come to love my Watcher in Pillars 2, but in the first game, the connection to my character just wasn't really there. For example, I despise the direction Dragon Age took, with a new protag each time but BioWare still cynically wanting to have their cake and eat it with all the returning companions, Dragon Age felt like a poor man's Suikoden because each game's story was never closed out properly and/or ended with a lead in to a potential sequel from which the original protagonist was noticeable absent. Getting back to the point; Pillars lacked both a compelling core story, hook or my attachment to my character. In that sense, I suppose it's quite impressive that the sequel managed to actually draw me in like it did, but due to the first game's failings I wasn't immediately excited to play as the Watcher again in PoE2, when normally, that is an immediate buy-in for a sequel for me
I'm not going to say Pillars is boring because Josh injects boring shit into the game or anything like that but there was/is very clearly something that is causing this feeling in Obsidian's games when some unheard of team can produce Kingmaker out of nowhere and hit much closer to the mark. It often felt like I was playing a game that wanted to be BG2, but was frequently hampered and dragged down into Icewind Dale territory because it wasn't the same team making it. Contrast this with say Pathfinder: Kingmaker (which is a slow starter and the pacing ebbs and flows at parts) but was far more consistently enjoyable than Pillars 1. Even with Dragon Age: Origins, I was still fully engaged the whole way through, I strongly believe dialogue brevity probably helped here looking back at it.
Gameplay wise I had almost no issues with either game so I really don't think that's a factor, whether Josh loves to over-balance things or not, I don't think that plays into low sales at all.
TLDR: Pillars 2 is paying for the shortcomings and mistakes of the first game. Pathfinder had a solid enough story and enough build up to see me through the whole game, same with D:OS2 and I, along with many others are excited for their follow ups. Pillars 2 just felt like a "middle" game and the ending was... odd I guess. I'd buy another sequel if it continued to improve over Pillars 2, but as to how to correct sales numbers and match D:OS2 & Pathfinder's, I'm not sure what needs to be done, you can't retroactively fix PoE's impression on people.
