I went back and forth on whether or not I wanted to spend the time writing a review for this game and eventually decided it might help someone else that will regret spending money on it. I'll preface by saying I was a backer and played the beta.
This game is targeted at a VERY specific audience and does not make that readily available until after you have already bought it. That target is hardcore old-school RPG fans, I went in knowing this and was still disappointed. As much as this game wants to claim to be in the vein of BG1&2 it isn't. The combat isn't the same (turn based instead of RTwP), the story has no real villain or motivation besides some obscure upcoming catastrophe, the NPCs are forgettable, and there are only 2 fully fleshed out companions, neither one of them are very good IMO.
The combat system is simply not enjoyable. If I had to pick one word to describe the combat it would be "tedious". Sure there are a huge number of skills and abilities and spells and many of them can do combinations, but the actual flow of combat is superbly boring. First, it takes forever to move around while in combat, made doubly annoying due to the interface, so your characters will often stray into friendly fire due to an errant mouse click. Secondly the battles are overtuned, you MUST complete all the side-quests in an area or you will be out-leveled by your enemies by 2-3 levels. It also takes forever to resolve even a small encounter which adds to the frustration. The tooltips on spells and abilities don't really give you much information on how they function so you can wind up wasting a lot of effort learning spells that don't function as you expect or friendly firing your own party. The pace is beyond slow. Where RTwP you might spend a few minutes, rarely 15 on a single encounter, here you will spend 15-30 minutes on each encounter. And that isn't counting the amount of time you will wasting trying to recover after each fight or having to replay each encounter to actually get a desirable outcome. It simply isn't fun. Not to mention combat is poorly balanced, stealthy characters are mostly useless at present and certain magic users are very OP over melee.
The game is also very obtuse and provides almost no in-game information on different systems. You want to know how to acquire new spells and scrolls? Read the wiki. What about trading for new gear and spells? Read the wiki. Want to get a better handle on combat? Read the wiki. Want to learn about crafting? Read the wiki. Want to learn about companions and interaction skills? Read the wiki. I have played and enjoyed games before that have little to no documentation (Endless Space for one), but there has to be a payoff that makes the learning curve worthwhile. D:OS seems designed to make it so that you have absolutely no in-game documentation or tutorials for anything beyond the bare minimum, making the learning curve as high as anything I have encountered. But there is no payoff, just more tedium. The huge complexity in the game systems and lack of intuitive learning methods is just there to force you to spend additional time learning them instead of actually playing the game. Now my next complaint might bug people, but the lack of any kind of useful marker system or quest journal is beyond ridiculous. I could deal with the lack of quest markers, but the fact that the explanation in your quest journal is often "Find X person." (usually even less specifc than that) with no idea where X person might be found leads to a huge amount of frustration. You know how you felt with the completely useless quest log in ME3? Well that is how you will feel the entire game in D:OS. I spent several hours running around the first city trying to complete side quests just looking for the next person to progress the quest. After my 10th lap around the city and having progressed no closer to completion on half the side quests I was working on, I was beyond frustrated. And you damn well better complete every one of those quests if you expect to leave the city or you will be massacred by the enemies outside who are 2 levels above you; side-quests are NOT optional, you need the XP to keep up with the level curve of enemies.
As for the story it is pretty boring and has little direction. In the first 10 hours you learn about an impending catastrophe that will wipe out all civilization. There is no main villain, no big overarching objective, nothing to strive for. Just a huge collection of seemingly unconnected objectives to level your characters to do... something. There is also only 2 fully designed companions, crazy female warrior, and an ass****ish male wizard. Neither of which I cared for. You can get other companions, but they are randomly generated and don't have fleshed out back stories. So if you want actual meaningful interaction with your party you had better learn to like those two. Again it seems like a serious lack of direction when it comes to the narrative.
I was just overall really unimpressed. I am a huge fan of old-school RPGs: BG, NWN, IWD, Arcanum, etc... and have been playing RPGs for 2 decades. I really could not find anything to like here. This game is designed to appeal to only the most hardcore of the hardcore who do not want any outside help learning to play the game. I personally could not force myself to continue once I made it just past the first major city. There was no motivation to drive me on, just an expectation of more frustration and tedium to look forward to.
IMO if you are looking for an enjoyable old-school RPG I would wait for Torment or Eternity. Because Divinity:OS is just not worth all the frustration and tedium for little to no payoff in terms of story. I am really disappointed that I backed this game. Combined with Torment changing the combat system to turn-based (which I really do not enjoy) I will be seriously reconsidering backing games in the future. Which is a shame, because I had high hopes before release.