Warning, this a bit long.
The thing, is in terms of the game experiences themselves (characters, gameplay, etc), there really isn’t anything Bioware did that Black Isle (or Obsidian.. heck even CDPR) hasn't done better…
And yet, pretty much every Black Isle (and even CDPR’s first witcher game) were made with Bioware engines, perhaps supported with Bioware money, I don’t know all the details, but they are partnerships in a sense.
So while stating that objectively Icewind Dale 2 or Storm of Zehir are better than Dragon Age and Mass Effect is total sacrilege just about anywhere, probably even here, that isn’t to say Bioware hasn’t contributed in one way or another to the success of many video games and video game franchises. They built the engines used in PST and IWD, they built the engines used in NWN2 and their expansions, as well as in TW1. They clearly are (or at least were) highly skilled programmers and builders.
The best Bioware game, although I must confess having not played all their games, really probably is Sonic Dark Chronicles, which is kind of the hopeful aspirational side of the company, avid hyper cerebral fans of a Japanese video game franchise that while not, not totally mastering good game mechanics, basically make for a unique sort of romp, substituting gameplay aspects for immersive ones at a less than 1:1 ratio, but not enough to become unrespectable and you can certainly feel the kind of positive energy.
Lets be real here though, we all know at the same time that Bioware games themselves are really super cheesy and stuff, and with so many generic stereotypes and tropes and whatnot. Disciplined and focused samurai ninjas, spacey and easily manipulated bards, over aggressive and sexy pirates, autistic robots exploring their human and emotional side, flamboyantly dashing mages and rogues with a heart of gold, and all together in their hope to save the world from the clutches of evil Mr. Cyborg or Dark lord or whatever.
Plus they have that back and forth teasing romantic stuff like it was scribbed from 10 things I hate about you or some other mid 90s movie that reflects (to be kind of blunt but fair) a pretty childish view of romance….
And yet even then, you can see the purity and aggression with which they derive things is actually kind of impressive way, it’s like they’re amazing copiers to the point where you don’t even care that their copying so much…
But ultimately, those are skills better suited to something else, such as programming and stuff rather than the characters and essence of the experience itself. I make an exception for Portalbendarwinden and their sense of humor though.
In essence, Bioware was (coudln't really say still are, since they don't make engines anymore for example) really good at engine development, programming, navigating those kinds of things, but it’s Black Isle that really put the heart and soul into the CRPG genre and made it burn with energy and resonance.
Then eventually they split apart and Black Isle/Obsidian is like perpetually on the brink financially and Bioware produces things closer to interactive dramas or visual novels than CRPGs (and doesn’t even make engines anymore). It’s a bummer.
I would say “ever since Bioware decided to go it alone” but it seems it’s really probably safer to put EA for a lot of that, and that they were truly the ultimate wedge that spurred the two companies to move apart.