As for size and complexity, there were original Doom levels that surpass the 2016 levels in every quantifiable measure. Larger maps, huge mazes, etc. All thanks to the WAD system that allowed Doom to have such long legs thanks to community driven content. With the new graphics system of 2016, community generated content was just never going to be a real thing with 2016. That is where 2016 and the original differ the most. As for unwanted RPG elements, 2016 at least has a mode that ignores that and dumps you into any level you want. To your point though, the RPG elements did alienate some fans of the original games, which goes back to my original point.
2016 was moderately successful. It got a lot of praise just for being stylistically Doom in every way that Doom 3 wasn't. But I don't think that Doom 2016 counts as strong evidence that HL3 could be made in a way that satisfies fans of the original games without alienating younger/modern gamers.
2016 was moderately successful. It got a lot of praise just for being stylistically Doom in every way that Doom 3 wasn't. But I don't think that Doom 2016 counts as strong evidence that HL3 could be made in a way that satisfies fans of the original games without alienating younger/modern gamers.