Yes if you want to support the development.
No if you just want a game to play. It’s incomplete, and your progress won’t move over to the later/final releases.
Larian is a great developer, and it’s awesome we’re getting another Baldur’s Gate release; but asking full retail for only a piece of a game is asking a lot from the average consumer.
If anything, they should have given option to pre-purchase, and developed a special, stand alone piece of content, consisting of a handful of hours of gameplay that highlighted the mechanics and tone of the game.
Not just the initial piece of the main game, of which your progress won’t even move over to the final release.