Actually i think there was enough drama, alone from audio that played during Nelo Angelo's demise, where Dante remembered their past. I think it has much stronger impact that explanation like "it's sad, because---"
I would disagree. Vergil was not a character on people's minds for the majority of the game, and even with all the little hints of who Nelo Angelo might be, he wasn't a major player in the plot. We as an audience are told outright he is Vergil after Nelo Angelo's death, but there is little impact to be had, because Vergil has no character development - he's the supposedly dead brother and nothing more (until DMC3).
Let's compare Nelo Angelo/Vergil to the most famous familial twist of all: Darth Vader/Anakin Skywalker. Before the reveal at the end of Empire Strikes Back, there was quite a bit of information detailing who Anakin was, which was contrasted by the evil that Darth Vader was, while also pinning the blame of Anakin's death on Vader. When we find out that they're one in the same, there's a sense of shock to be had because we knew so much about the hero Anakin to find it tragic that he had become the villainous Darth Vader.
With Vergil in DMC1, we know literally nothing about him other than he's a dead twin brother. We have lots of hints that Nelo Angelo is Vergil, but those don't paint us a picture of who Vergil was, just what Nelo Angelo used to be. As I said, DMC3 retroactively adds a bit of drama to the Nelo Angelo twist, but even then they did nothing to explain why Vergil was even alive in the first place.