F1 is the only valid preference in terms of overall quality superiority.
Duh.
G2NotR is superior to G1 in every way. Including pacing and content padding.
Yes and no. G2NotR has insane spikes in quality but also terrible lows.
The city itself is pure incline but the Valley of Mines is utter garbage. Everything after Valley of Mines is utter garbage.
The expansion additions story/lore wise are cool in the beginning but once you travel through the portal all NPCs from the main map forget it ever existed.
Making the game harder is awesome of course but it also introduces some subpar shit to the character system. Meta-gaming stat allocation and stat boosters is one.
Turning normal damage into grazes and critical hits into normal damage is another. What is this shit ? Pillars of Eternity? I need to increase a number and pray to RNGesus that my normal damage procs ? Shit idea.
G1 also has endgame problems but at least it's over quicker.
In both games you become overpowered and finish all the cool quests roughly at same time leaving nothing but a slog to the end from that point on. The difference is that in G1 that slog is about 3-4 times shorter.
MM7's only advantage over MM6 is having refined the rather raw role-playing system introduced in MM6. MM7 is vastly inferior in every other way except combat and itemisation (which haven't changed) - exploration (the biggest factor in MM series), lore and questing, magic system, even GRAPHICS, of all things (just compare the dungeon visuals in MM6 vs MM7). The only reasons why MM7 is more popular is because it's much easier, and because it's heavily tied in with insanely popular HoMM3 in terms of lore and graphics.
This is just nostalgia bullshit. Exploration is over once you can cast fly. This happens way earlier in 6. Where's the great exploration in sweeping fog of war off the mini map while raining death from above.
Lore and questing ? Nigga please. Sure there's some cool shit here and there (mostly leaning on the established lore) but there's a lot of generic fetch quests that serve no purpose but being filler.
Magic system? Are you snorting coke? In 7 there is at least a short period where you have to use low level spells creatively, in 6 the main plot hasn't even really started and you have most nukes at the ready. Sheet.
Graphics are more coherent in setting a tone in 6. True.
And finally we arrive at Codex favorite meme - "M&M6 dungeons were the shitz! M&M7 dungeons are the suxzors"
This is a nuanced discussion. The best dungeons of 6 are better than the best of 7. However there are dungeons in 7 that have a better visual theme going for them than any in 6. Some dungeons are really small in 7, you can barely call them dungeons. Some dungeons in 6 are just long for the sake of being long become boring.
Overall M&M6 comes on top on this point but not enough (for me) to disregards how fast the challenge fades away leaving only 'go through the motions' boring gameplay.