Zeno Clash is the closest thing in my opinion. I don't think they take anything seriously, but it's not necessarily a flaw.

By the way, Hexen II initially had a different name. The game was later re-branded to Hexen II. This explains why so few things connect Hexen II and the other games, and why the setting is so generic medieval fantasy complete with Devil as the main opponent.

The 3rd game in the trilogy was meant to be Hecatomb.
http://www.johnromero.com/wiki/index.php/Hecatomb

Another bit of trivia - Heresiarch from Hexen was initially meant to be the final boss. Check out the ending animation of Heretic. And Korax looks more like D'sparil's mount, not a boss. I read somewhere that was the original plan and they've changed it over the course of development.

Hexen, while a game with deep flaws (extreme switch hunting and "haha, you're stuck!" puzzles, repetitive combat, lack of class diversity, lame instadeath traps with no warning) is a game with charm. I made a gameplay mod for it, but then realized nobody cares about the game anymore and stopped developing it. If you're interested in it, I can send you the latest (unfinished) version. Highlights include:

- Disc of Repulsion actually pulls enemies closer and down (flyers) if you're a warrior

- Hammer of Retribution is a huge mana hog, but is reusable because it produces 20(depends on difficulty setting) mana where it hits. This was done to change the playstyle of Warrior class to be more in-your-face while still allowing him to kill enemies at a distance.

- Quietus, the 4th Warrior weapon, has a railgun-like effect meaning projectiles pierce multiple enemies. This finally gave it a niche and it's a great weapon against swarms up close.

- spiked gauntlets (fists) only have strong punches (called "critical hit" in the engine) for finishing blows.

- flechette items work more like grenades and require good timing, they explode 1 second after first bounce

- sapphire wand of Mage is severely nerfed in range to make room for other weapons.

- Frost Shards deal 50% more damage

- Bloodscourge (4th mage weapon) overhauled. Each projectile is guaranteed to home on a different enemy. Second, it deals extreme explosive damage, especially to the user. With Hexen's cramped level design, it makes it THE best weapon in the open and extremely dangerous in corridors. I also modified the homing algorithm, now it has no problem hitting enemies on high ledges. And a cosmetic effect - big clouds of smoke. Tim the Enchanter would LOVE it.

- Wraithverge (cleric's 4th weapon) no longer attacks inactive enemies through walls, which used to wake half of the level and was obnoxious. Additionally, instead of killing enemies outright, it reduces them to 1 HP. Nice synergy with mace. Ghost AI makes them ignore crippled enemies.

Monsters:
- afrits (fire imps) have short-ranged flamethrower with interesting projectile physics.

- stalkers (water lurkers) have very mean and currently unbalanced attack where they grab and immobilize you when they emerge. Any hit will break the grab.

- fixed obnoxious bugs with Dark Bishop and Stalker Leader which caused them to attempt shooting through walls (sent the patch upstream)

The goal of the mod was to make enemies and weapons more varied and interesting, and to challenge a modern FPS player. It utilizes the obscure Vavoom source port, which is technically very advanced, has engine written in a scripting language, but is unfortunately quite buggy and poorly documented. I had some more ideas I wanted to implement, such as alternate effect for Chaos Device (shuffles positions of all monsters on the level using Knuth's algorithm). Overall, I love how the 4th weapons of Cleric, Warrior and Mage turned out, they're now a joy to play with (especially mage).