Do you remember the good old times when PC games were still PC games? No need to just remember anymore.
Simply put, the storytelling is superb. The plot might be clichéd (a great evil arises periodically and threatens to destroy the world), but from this simple idea Bioware managed to get an engaging storyline in an original world. There's a lot of party banter, lots of conversations with NPCs, and all of it is well written and well voice-acted. However, if you don't like your games to be cinematic, you might feel bored. Your character is mute, though, which is a slight letdown after Mass Effect, but hey, you get to select your responses with numbers on the keyboard and not just with the mouse. How long has it been since you could do that in a game?
The combat system is a cross between a typical MMO model (active skills/spells with cooldowns) and the classic "real time with pause" model from Bioware's earlier games. It works great, there's a lot of tactics involved, although it can get tedious to micromanage the mages due to "friendly fire" from AoE spells, especially in longer battles. Luckily, the PC version includes an isometric (bird's-eye) perspective which makes controlling the battles much easier.
There's "only" three races (human, elf, dwarf) and three classes (warrior, rogue, mage) to choose from, but there's a lot of skills/spells available, both general and class specific and four specializations for each class, so it feels like enough in the end. Also, your race/class selection (the titular origin) determines your starting point in the game (it takes about 1-2 hours before the story gets to the same point for everyone). The classes themselves are pretty self-explanatory, warriors do damage and tank, rogues pick locks, disarm traps and deliver great damage in combat but are squishy, and mages zap with spells, do crowd control or heal and are even more squishy.
The gameworld isn't open, but includes a large number of quests, ranging from deep emotional ones to simple Fed-Ex for various factions. All of them are satisfying and help bring life to the world.
The graphics are probably the weakest point of the game. Everything is either murky brown or murky grey, and leaves a general impression of "meh". However, in a game like this it doesn't matter, so I won't spend too much time on it. The characters aren't that bad, however, and the facial animations are quite good generally – just don't be scared when one of your party member s starts singing.
Bottom line: It feels like a PC game, it plays like a PC game, and it's a real spiritual successor to the Baldur's Gate series. If you're a PC/RPG purist like me, get it. Now.