I finally got through to the end and did the final boss, after almost three years. The game does improve - the first two or three levels are slow but once you unlock the ballista, chaingun, double barreled shotty and some upgrades the fun really moves up a notch.
Having said that - I do still prefer Doom 2016. I still don't like the chainsaw mechanic. Grenades are a complete waste of time. Way way way too many upgrade trees for various things. And the marauder was just a complete let-down given how hard he was hyped. The gladiator and maykr fights were ok but the icon of sin was a mess, it's just a messy survival fight, trying to figure out which part is still alive whilst you're being assaulted with colours from everywhere.
I'm not sure I have any inkling to replay it or bother collecting things, which is a shame as I still drop into 2016 from time to time.
I'm wavering around a 6/10, whilst i'd consider 2016 an 8/10.
But, at least I got it done!