Does Diablo 3 still have long haul elite fights like this?

Grim Dawn is a single player ARPG (there is the option to go multiplayer, but it's mostly single player focused) that runs (afaik) on a singly improved and heavily modified version of the engine that Titan Quest used.

The world it is set in (I... honestly can't remember the name. I suck at remembering names) a world that was overrun by the so-called "Aetherials", which are somewhat like spirits, but were banished to their own plane of existance a long time ago. However, something caused the veil between the worlds to lift for a moment, so they invaded what was originally their world. There's also (normal) gods, the witch gods (former humans that ascended to godhood) and the dying god C'thon. C'thon was the first to create life, so the other gods became jealus and tried to kill him. Since he's immortal, he remains in a perpetual state of dying-but-not-dead. They then used his blood to create all life and then banished him and his creations. He has a cult though, focusing on blood rituals, trying to gather all blood there is to return it to the "rightful owner" if you will.

Those two factions, the Aetherials and the Cult of C'thon serve as the main antagonists. Speaking of factions, there's a lot. Almost every bigger city is a seperate friendly faction and every larger enemy type is an enemy faction. There is also 1 (or 2 with the DLC) neutral faction which you can either make your ally or your enemy.
Depending on your standings with an allied faction, you can buy special items in the faction vendor. On the other hand, the more enemies of a certain enemy faction you kill, the more dangerous that faction will become. It starts harmless with slightly increased spawn rates, but then elite enemies or champions will become more frequent. At the end of the spectrum we have nemesis bosses.

Those are some of the ultra bosses I mentioned. They are extremely tough, they hit like a truck, have special moves and most importantly, give metric fuckton of look and exp when you kill them. They are quite diverse, ranging from extremely strong humans over a giant insect in a hidden path in a hidden quest to an avatar of a god. Make no mistake though, they are all quite similar in power. It can take quite a while to beat them down, even more so if you have to kite them (which you most likey have to do) and can usually wreck you in a hit or two if you aren't careful.

The skill system is almost exactly the same as titan quest, at 2 seperate level thresholds you can choose 1 class, so you have a combination of 2 classes in the end. The combinations can result in all kinds of shenanigans, melee spell caster, ranged spell caster, ranged or melee attacker, summoner, reflect build, etc. You can then invest skill points either in the class itself to gain stats and unlock different skills, or in the skills to make them more powerful. The skills can also have modifers that add to them, kinda like more specified support gems. There's also auras, but they do not only reserve energy, but sometimes also energy regen. Also quite interesting is that the offensive skills are a mix between PoE's spells and attacks, they have a certain flat amount of damage they deal, but can also have scalings based on your weapon damage.

Then there's the pantheon system, which is somewhat more akin to a classical skill tree. Basically star constellations which you can allocate to gain some stats or semi-active skills which you have to bind to your active skills. You get points for that by finding shrines in the story and purifying/repairing them.

The story takes you through I think 5 acts, but the game doesn't call them that. The community simply named certain parts of the game "acts" because it's easier to pinpoint story points that way. There's 3 playthroughs though, so it can get boring at playthrough 2 or 3. The game world itself is always the same, except from the locations of some small roadblocks or caves that can differ between characters and playthroughs. It does fit quite well though, it allows you to easier find certain locations, or even helps you to remember paths to secret locations.

For the items, you have the usual normal, magic, rare, epic and mythic items. There is a built-in loot filter you can use that filter everything below a certain rarity. Here is where it gets interesting though, since there are quite a few so-called "monster infrequent drops". Those are rare items that can have some unique effects, modifying certain skills: converting the damage type to a different one, adding a stun/freeze/whatever, giving it a higher damage scaling, reducing the cooldown and more. They always have a stat that normally doesn't appear on that type of gear though, so they can be quite valuable with the right prefixes and suffixes. Epics and Mythics are like PoE's uniques, though there are also item sets. Nowhere near as ridiculous as the ones from D3 though.

I probably forgot quite a few more or less important things, but yeah, that's some info on grim dawn. It also has a LOT of secrets to discover including a few secret quest lines as well as a ton (and I mean a TON) of lore. The game can get pretty tough, especially in higher difficulties and there is a death penalty. However, by walking to the point you died and clicking on the gravestone you left, you can get most of the xp you lost on death back.

It's very different from both PoE and D3. The item system makes a lot of drops a big deal more interesting than 99.99% of what drops in both PoE and D3 together. There's a lot to learn though, there are many, many things you have to take into account if you want to make a really successful character. Or you can just go, start a character and see where it takes you.