How exactly was he drastically different from his DMC 1 self? Someone enlighten me.
That's how he's different from DMC1. The funny thing about this thread is that I didn't think I would ever see the day where someone raises the argument that DMC2 and DMC1 Dante are not all that different. That's just bonkers. DMC1 Dante had serious moments, but he's also the guy who had fun in juggling a motorbike with pistol bullets, engaged in banter with bosses and was playfully cocky throughout his whole journey, where's all that in DMC2? Like, one line in the entire game (the crown line) doesn't cut it. A lot of the defining characteristics of Dante are just not there.
Now as I said, if they added context to this, showing why he did a 180 in personality, I wouldn't have minded. I actually think it would have been pretty interesting. Look at Prince of Persia. In Warrior Within he's broodier, more ruthless, less insecure and more violent. But they surrounded this personality change with a believable context, he had been chased by a fearsome creature for years trying to kill him for a mistake he made for his pride without quarter. That way, it comes across as an actual progression in character rather than the developers just looking like they don't know who the character they're portraying even is.
I've heard that DMC2 was originally meant to be another game altogether, and that they turned it into a sequel to DMC1 after its success, which would also explain why DMC2's production began while DMC1 was still in the last stages of its own development. If that's the case, that also explains why it feels so disconnected from the rest of the series as a whole, not just when it comes to Dante's character.
DMC2 was just a mess ever since its conceivement, having an identity crisis, swapping staff, trying to patch things up at the last moment. Alienation is bound to happen in cases like that.