I mean really, really boring. The battles are all tedious and take too long. You get some new crap... big deal.

Regular mode was a lot more fun for me.

Many experienced players want to increase their gaming experience/challenge once the game has become a bit boring. As we know, this can be done in various ways. For example, with mods (not too many for IWD though), with increased power/difficulty (HoF), or both.

I also didn't favour HoF or insane modes (e.g. in BG2) for my own games.

HoF insane mode requires a totally different strategy. Melee becomes a thing of the past - the more spellcasters you have the better. And you better have single class or near-single class characters, otherwise your damage spells are too low level.
Melee is something you use in minor encounters and to clear up remaining enemies after the main battle has been fought.
Mostly you need spells. Here are the best strategies in order of effectiveness:
1) Otiluke's Resilient Sphere on one of your own, AFTER all enemies targeted it. You can then create a killzone where enemies neatly walk into your area damage spells. This will work in even the most difficult encounters. If you see this as cheese or abuse of the dumbness of the AI, then I'm afraid I have no viable alternative for the most difficult end battles. The roof of the horde fortress was the best Otiluke battle.
2) The Holy Word spell give you 6 seconds to blast frozen enemies. There's no saving throw, so it always works against evil enemies. Keep a mixed-alignment party out of the area when casting. It works against big groups in combination with saving-throw-lowering spells and Mass Dominate - whatever's left can be killed in melee by their own!
3) Summons are enhanced as well as enemies, so they'll take on quite large groups, and you can back them up with certain enemy-only area spells, ranged weapons or even melee if you like. This tactic is insufficient for many large battles.
4) Have your melee character run forward, but keep running around instead of engaging. This allows for ranged attacks and certain spells. This works for small groups, and there's a risk some enemies will target others eventually.
5) First create a barrier with Web, Grease, Entanglement, Slow, Hold etc. This only works if enemies are coming from 1 direction. You can blast them for a while, but strong enemies will make it through eventually. This tactic becomes useless toward the end.
6) Direct spellcasting without Otiluke or a stalling zone is difficult to pull off, enemies approach you quickly, and if you're entire party isn't spell resistant, you'll have an even harder time.

IWD2 is a hard game, especially in Heart of Fury mode. The thing about it is that getting immunities is very difficult (Otiluke is a rare exception), mostly you must suffice with a mild resistance. Even Stoneskins don't block all damage all the time. It makes the battles more realistic (for a fantasy game...) than BG2, where spells give complete immunities.
There is less of a sense of power, even for a high level mage, because you are always vulnerable. Also, the roles are reversed, I think. In BG2 you are fighting powerful mages, and the best way to defeat them is kill them quickly in melee. In IWD2 HoF you are the spellcaster fighting off hordes of melee monsters. But that's just my experience. If you have a melee party, I can understand why you find it boring - it's all hack 'n slash. And your single mage will need to rest often to replenish his often used spells in HoF mode, that's a bit tedious. You'll be rearranging your spell picks and resting half the game!

Try my spellcasting party, it's great fun!
1) CN Female Drow; 18-15-16-5-15-11; Bard 5 / Tempus X; improve Constitution
2) NG Female Drow; 18-18-16-5-18-5; Fighter 4 / Lathander X; improve Constitution
3) CE Gray Dwarf; 18-18-20-3-14-1; Fighter 4 / Barbarian X; improve Constitution
4) LN Human; 18-16-18-3-18-3; Monk o/t Old Order 1 / Ranger 1 / Druid X; improve Wisdom
5) LG Human; 16-18-18-3-3-18; Paladin of Mystra 1 / Ranger 1 / Sorcerer X; improve Charisma
6) NE Deep Gnome; 12-20-18-18-5-1; Ranger 1 / Rogue 2 / Illusionist X; improve Intelligence

I've put an obsessive amount of thought into composing this party, and I'd be happy to explain the choices I made if you have questions.
Check my post under "Icewind Dale II Useful Info" to download a detailed guide I wrote.