D:OS2 was a great fun. It is a bit wacky at times, but i liked it. I think it is using a ruleset completely made up by Larian, it definitely isn't 5e. The gameplay is very similar to BG 3, but there is A LOT more options for interactions with environments and surfaces, it has telekinesis (teleport oil barrel on top of enemy and make it explode, or teleport enemy into lava, etc.), you can do some insane and fun things if you want. It isn't as cinematic as BG3 (where every conversation is basically a custscene, D:OS2 dialogues are just text based, but still voiced). You can play a custom character, or pick one of 6 Origin characters (each has their own backstory that often-ish affect situations in the game, takes you to different special places, or provides various different options and reactions/dialogues). You can play alone in Singleplayer, or in Multiplayer (up to 4 players) as a Coop or PvP (not 100% sure about the PvP - i did split from the party at some point to test it, and i could fight my friends, and play the game in parallel with them, but i did so only for a while, so i do not know what happens if you try to progress into next Act while others remain in Act behind you or if that is even possible).
It is an older game, but the graphics still holds up (for this type of game). The D:OS2 Definitive Edition is ~60 GB download, so you may still struggle a bit.
...watch some official trailers and other official videos - they should provide enough information (and without spoilers) for you to make up your mind as to whether it is a game you would like. I think anybody who likes CRPGs with turn-based combat, should definitely have a look at this one.
Here is a good short video that should give you some idea: (crap... just watching it makes me want to play it again, but i still have BG3 to finish :-D)
