I played many times Act 1 in EA but never the Grym fight, I played after release one playthrough in Balanced/Tactician until lvl 10, leaving out the Grym fight. Then I started in Honour mode, after I had watched someone starting Honour mode on Youtube...
My party consisted of Gale, Shadowheart, Astarion and my main, Warlock/Sorceress to be. Act 1 was quite easy because I knew it by heart, but I had to run away from the owlbear fight (mostly because I made the two siblings hostile by carelessly touching them with an aoe spell) and from the Gith patrol fight (I had two dead and one in Hold Person before I could even roll the dice; from then on I knew that the most important Honour mode stat is initiative).
Doing Grym first time in Honour mode was not the best of all ideas. I needed about 1.5 hours for the fight, two times I was near to give up (for example once when I tested wether running through the lava would be that bad), but then in the end I survived even with three on the legs. The most difficult fight I had in the whole game till now.
In the Creche Astarion now was a ranged Fighter/Thief, Gale an Evocation Wizard and Shadowheart a Tempest Cleric, my main a Thunder Sorceress. I was especially in some horror of the Captain fight (one of the rare situations I had had a wipe in my first playthrough), but it was ok.
Act 2 was not that difficult, I did all quests and all bosses to get xp as much as possible and was lvl 9 before Ketheric as far as I remember. Act 2 contains my most hated event in the game, the abduction of Isobel. My plan was to stop playing in case I failed. Wether they toned it down since shortly after release a lot or I was extremely overprepared, it was a breeze this time. Ketheric's fights were not that of a problem, I had however left Jaheira out to not endager her. And it was almost the biggest problem of the hive fight to keep Aylin alive. Beware, the Ketheric encounters allegedly got more difficult with Patch 6.
Act 3 was mostly new for me as I never played it outside Honour mode, but manageable. I ran away from the Ethel fight, without any reason I noticed later, because I thought the shown hp of her billion copies were the real hp. I ran away two times from the Ansur fight; after my ingenious plan for a second attack by superior char placement had failed miserably, I used the I-Win-globe for my third and successful approach. The fight against Raphael went worse than I had hoped and Hope died in it, that's a shame. My group had changed during Act 3 btw, as now Jaheira (skilled as Paladin 8/ Bard 4) was in the place of Astarion. My main had a Warlock 2/ Fighter 4/ Sorceress 6 crit build.
There are two fights left, Orin and the brain. I somehow ran out of steam however (or are frightened too much ...?), parked my run and started a Custom mode one as Dark Urge, important for me with more saves (for better experimenting, was the most fun) and some mods which unlock Honour mode features, make enemies stronger than Tactician/Honour mode, remove Wet's vulnerability effect and randomize the loot. It's also not allowed by house rule to use Haste on a caster. I think Larian should extend the Custom mode area a bit similarly.
Generally I used in the Honour run almost all the bad stuff you should actually avoid, like attacking from stealth, Haste, vulnerability from Wet and even in one rare instance a barrel. I thought if the game has an "unfair" mode, I can use unfair game features. I did not sink low enough however to use a strength potion on strength build chars, except once for getting Phalar Aluve. I also did not metagame, so I made all the dialogs before fights where you don't know wether the talking partner is hostile or not (exception: Giths in the creche because I was on a run to kill all of them after Shadowheart had disemboweled Lae'zel due to unlucky dice rolls). I do not use shove.
As my preliminary result I think Larian got Honour mode in a good place. It is tough but not too tough and not too easy; it's manageable even if you get unlucky sometimes. The friend of you if you get unlucky is the best and most overpowered item in the game, seldomly mentioned, the healing potion.
