I don't know what it is. I mean, the game is definitely much more challenging, but it takes so long to bring enemies down that I'm finding it quite boring as well.

Anybody else feel like this? Anybody disagree?

I tried it briefly for icewind dale 1 and I agree. It kind of annoyed me too because I felt like only casters could do well and even though I like casters a lot, I didn't feel like much of a hero relying on summons to win every battle.

Personally I play on insane and I find that pretty challenging, but still doable. Although I am finding because of the lack of good armor in iwd2 that fighters have a tough time getting a decent ac. You almost have to do an all-or-nothing approach with ac in this game. Either you have it or you just ignore it completely in favor of hps and damage. I'm starting to think the latter is the best approach to this game unless you cheese it up with ridiculous ac decoys. But I find those characters incredibly dull and boring.

It was fun to build and play a high level party and to have meaningful resistance to test the party with. HoF is a nice addition but after several times through (twice solo and 3 or 4 other times with parties) it became boring for me.

I've played the core rules campaign dozens of times and am not completely bored with it yet.

Same, can't find the drive to even bother trying it anylonger. I find it annoying enough how long certain enemies last on normal mode, going into HoF just annoys me.

Soloing is kind of boring already and replaying the same campaign with the same team, just on a higher difficulty level, would feel boring to me - I don't even try. Besides, employing complex tactics to defeat apparently simple and basic monsters (e.g. PowerGobbles) is boring too. Respect to those guys who do it, but I can't. I'd rather just play something I haven't yet.

HoF is boring because it takes hordes of summoned creatures to do your party's dirty work. Plus HoF items are so overpowered that it is utterly silly. Not that these items are going to make that much of a difference when facing three goblins at the same time with a level 20 character in melee.

HOF isn't that booring if you do it without summons (usually requires a high-AC character). Summons are ok to use sometimes but playing through the whole HOF and having to summon for each battle would be really booring.
But I really prefer playing normal mode.

HoF is boring, because it requires degree level munchkinism. The sheer amount of work that goes into "UPP's" (both Jukka's and the original) is ridiculous. I swear that by Masters thesis was shorter than Jukka's guide. I use maths to swing odds in my favour playing RPGs, but that's just too much. If you can't play the game without either summoning legions of meatshields or relentless powergaming, where's the roleplaying? It's supposed to be a roleplaying game. Even on Normal mode, battles often end up with your party sitting behind Undead legions flinging spells and arrows at the enemy, rather than doing actual fighting. Sure, Baldur's Gate was easier, but you could get through it using just about any character with a variety of tactics, which made it fun. IWD2's challenge is too restrictive and linear.

In IWD2 you can play through normal mode even with a party of only badly-multiclassed rouges with no sneaking abilities. I don't agree that it requires any special tactics and I almost never use summons and the few times I use them are mostly for roleplaying reasons (my necromancer sometimes likes summoning zombies and skeleons in places where you can find other bodies, feels almost like he raises them).

And there are people (I guess I'm not the only one at least) that really loves planning parties to be as efficient and fun to play as possible while still following some preset roleplaying guideline.
All my parties are like that.
One example is my last "full play through"-party where I had decided that it should include an evil gray dwarf priest, a confused deep gnome, a dark-goblin sorcerer, a priest-like halfling and one more social thief-like halfling and a gnomish spellsword. Then I started planning and came up with a really powerful party that followed this theme and was fun to play.

I don't think pure powergaming is too fun, but roleplaying combined with a lot of powergaming usually gives the most fun parties that can beat the enemies in lots of different ways.

I agree with The Magpie's view. The amount of power gaming necessary to complete HoF takes most of the fun out of it for me. Besides, to do HoF, I will have already gone through the game with that party and roleplayed the appropriate options. I personally just don't see the attraction in roleplaying my way through in the same way with tougher enemies.