Okay, currently halfway throught NM, still on p8. I thought I'd maybe have to tone it down for bosses, but no. After converting my other offline chars to ROTW and giving him the needed leg up with vipermagi, spirit, lore, magefist, rhyme and insight on merc (soon spirit shield, shako, CoH on merc) I'm just completely tearing through everything that isn't immune to fire.
Ring of fire is a CC tool, although it can be used as your main source of damage until you get the flame wave.
Flame wave is just broken in open areas. Suffers in corridors and makes you feel woeful if there's stairs or any obstacles (jail bars, barrels, anything), you will absolutely hate normal Arcane Sanctuary.
Apocalypse at higher levels covers almost the entire screen. Unfortunately it appears that its innate bonus of reducing enemy fire res for the cast can't break immunities. Otherwise, it's a big nuke and wipes groups with ease despite supposedly meager (2-3k fire damage at level ~15) damage. You will want that flickering flame and fire sunder charm on Hell, definitely.
I initially respecced into miasma/oblivion at the start of act 4, but these spells are so lackluster on their own I just invested into fire again. Feels like they're a panic button for when you find fire immune enemies. Oblivion has a pull, but ring of flames just does that job better.
Summons are alright, but
need those +all skill modifiers on your gear, otherwise they will have paper durability. You will want to reach 20 with summon mastery, since every 10 points nets you an additional active summon, and you can have a combination of any of the three (possibly four and five at 30 and 40 investment?). They do very little damage, unsurprisingly, but their role is purely support. The goatman tanks and has some crushing blow, the tainted gives your party fire resistance, and the defiler automatically curses enemies with a share damage debuff. All your summons are very aggressive, relentless, teleport to you
very quickly (unlike the fucking mercs) and you can just resummon them for free. Worth noting that resummoning replaces your minions according to the order they were spawned in, so the oldest one will get replaced first, no matter what type it was - goat-tainted-defiler will turn into tainted-defiler-%newsummon.
The spells you can use to buff/debuff/sacrifice your summons I haven't tested, because that's WAY too busy and conditional ADHD of a playstyle for me.
Sigils are one point wonders, mostly. The one that cripples enemy speed, defense and damage is probably the one you will be using the most.
And on an unrelated note, I think they buffed drops. Found around 30 unique/set items throughout normal at close to 0% MF.
this will literally take you like 400 hours legit.
More. This either resets if you change difficulty or every difficulty has its own tracker. Once I got to nightmare on Warlock, it was all back to 0%. If it's the former, then good luck trying to cheese with farming NM andy/meph/diablo and have fun throwing your PC out the window if you accidentally enter/create a game on normal/NM. If it's the latter, then 100% is impossible on normal and NM due to level zone caps.