I don't. Are there any that are essential or improve the game's general QOL?
I'd say mods are more about QOL, DLC's are more about gameplay.
Eran's list is more about QOL, and I'd agree with his suggestions on that.
As for DLC's, I have all the DLC's (though I never use snowfall maps, and natural disasters are switched off (I just want the helicopter services)), I have to say, it really makes it a different game.
It's been that long that I can't really remember what comes with what, but my top 2 would be Industries and Mass Transit.
Industries is the game changer for me, I play with 25 tiles mod and unlimited resources turned on. I will inevitably build my Industries DLC areas far away from each other, and tend to build local towns to support them, this immediately pushes you to build out an inter-town road network, think A-roads and B-roads. Once you have a network of A-roads, you can organically pick a location to build out a town (on the basis that the genesis of a town is normally a road junction (unless you've got a sensible coast or river). Over time you then fill in the green space inbetween and this organically forms cities. This can all be done with industry specialisations but the more granular nature and specific asset placement is more involving.
edited to add, when you start off building multiple smaller towns, I find there's more of an urge to build them with unique 'feels', and this leads you to go looking on the workshop for more appropriate assets (e.g. a smaller school, or more appropriate police station)
... basically I find it gives you a reason to build, other than just responding to the demand meter - even if it's just trying to minimize the import pie-chart and maximize the export pie-chart.
Mass Transit, I just like the options it gives you for moving people around. I tend to use trains a lot for freight so other options for people moving a welcome.
Beyond that, when you're starting to build bigger areas,
Park Life and
Campus again give you assets to build around and build for (for example, getting decent mass transit links into your University, Zoo or Theme Park).