My introduction into this series was Baldur's Gate: Dark Alliance, and it was one of the best couch co-op games out there. It's a sub-series that departed a bit from the main games, as it's purely an action rpg like Gauntlet or Diablo rather than D&D. And you only actually stay in Baldur's Gate for the opening bit iirc. It was so well done though. I played through with a friend and loved it.
I will pass on this though, and it is because of the combat system. I enjoy both action and turn based games, so I was open to Baldur's Gate 3 until I saw the gameplay videos. This particular brand of turn based combat is not for me. I get they're trying to recreate a table-top D&D experience, and that's a perfectly fine niche to fill, but it's not what I was looking for.
A new Baldur's Gate: Dark Alliance was finally announced last December. News has been sparse though, possibly due to COVID interfering with development. I think they actually dropped the Baldur's Gate portion of the title due to it not being all that connected to the main series.