It's modable. It has great storytelling, world building, lore and so on. The characters are mostly memorable. The skill, combat and item systems are from strong to "okay." A 100% run is easily 80hr of content. Not bad content you grit your teeth to do, but GOOD content. I still think about a few certain characters eleven years after I first purchased it. This is on the very short list of the top games ever made.
Good: 1.) Strong writing with copious humour. 2.) Good gameplay mechanics. 3.) Excellent skill and item system. 4.) Great gameplay for the price (70hr one run through doing 100%). 5.) Minimal hangups or "bad" spots. I experienced no bugs on my play throughs, but didn't care for the dragon fight mechanics at all, unfortunately. 6.) 70hr+ gameplay for Divinity 2 and it's expansion. Bad: 1.) The engine is kind of bad. 2.) Graphics aren't that great, though animations are okay. 3.) Voice work is questionable at times. 4.) The storyline though solid, feels like it's missing a lot of backstory. 5.) It's a little slow to start, but if you can make it to the hour mark you'll probably enjoy it. I'm picky and eccentric. This is one of the few games in the past decade I've completed in it's entirety. For the current price I consider it a steal, for the laughs I had alone. It's certainly in my top five or so titles of all time.
I don't own this title on GoG, but through Steam. Overall it's one of the most entertaining (mechanically, story and general humour) wise games I've ever played. Good graphics, exceptional game play mechanics, nice characters, writing and such. It's very silly, in fact, it redefines silly. It's pretty mod friendly, as well, which is nice. I strongly recommend this title for the current price, the entertainment it can provide makes it very difficult to beat.