I've sunk 400 hours in across the last 2-3 years and 'finished' the campaign many times at this point.
The game is pretty free of bugs, has decent enough storytelling elements and the classes/characters have really enjoyable progression along with great crafting and a hefty amount of legendaries/uniques. If you're looking to completely max a character from 1-100 with mid-good rolls on all slots, you're looking at probably 100s of hours. I'm sure someone can cut that time way down but for average player it'll be a long while. The monolith and arena content with the target farming and etc stays interesting enough given the risk/reward balance you do for your item farms.
Game is closer to grim dawn with the expansions than D3 imo. It's a bit floatier than D2/GD but not enough that I'd consider it worse, just a different feel, depending on the build. Some classes are very mobile and don't need to stop to cast/attack, others can be more stationary. Just depends.
...