Well, I never actually completed MM6. Didn't like the changes when it came out. Muddled around with it & quit rather quickly. But I did complete MM1-5 when each of them came out.
MM1 felt like a monstrously huge game at its time, and I loved it. A big fantasy, monster, magic, and quest-filled epic adventure. And MM2, with slight improvements, felt just as grand.
But then MM3 came out & blew them away. Being able to see monsters from a distance & shoot arrows or cast spells (casting becoming so much easier overall) at them before they got to me, plus the whole GUI-based upgrade...it was a phenomenal step up.
And MM4/5 being able to combine together into an even larger world with more quests, and some other improvements.
So I bought the set from GOG, intending to play 1-5 in order all over again. But I have to say, MM1 just disappointed. Only being able to save at the Inn was a huge pain in the neck, monsters were much more difficult, spellcasting was frustrating (always looking up the "spell numbers"). Just knowing MM4/5 was readily available, with all its improvements, I couldn't take it anymore. I started MM4/5 instead.
I knew going in exactly what MM1 was like, I played it 25 years ago. But I couldn't enjoy it anymore. The story & the leveling up was always fun, but I just couldn't get into it. I even grabbed an MM1 character editor & gave my characters great weapons/armor/stats and high levels, but it seemed like some of the monsters were still ridiculously hard (Succubus Queen & Caryatid Guards, for instance, who can only be hit with magic). I'm disappointed that I didn't enjoy it like I used to, although there's no real fault to place on anyone/anything. I mean, I played it & finished it once, its obviously not impossible, but I think MM4/5 kinda ruined me for MM1/2. Still, $10 for MM3/4/5 (since I doubt I'll play MM1/2/6) is VERY well worth my money. I can't say enough good things about MM3/4/5.

I had a different experience because I'd only played 4-6 before. This pack gave me a great chance to try to earlier games, and I actually enjoyed them quite a bit. I was afraid that the first game would be too frustrating because it was so old, but surprisingly I was actually impressed with how much the author was able to do given the technical limitations. I've just started the second game now and the improvements make it even better.
Looking up spell numbers in the first game is annoying, but I found that with the right tactics the monsters aren't TOO bad. Turns out that monsters like Caryatid Guards can actually be damaged by magic WEAPONS as well as spells (any weapon with a "+" on it). Once I figured that out things got a lot easier. And most of the REALLY tough fights (Succubus Queen, large numbers of dragons, etc.) are actually optional. They're really only there for those who really wanted to max out their party and get crazy high levels. My biggest complaint is that almost all the loot is randomized; I was hoping for some places where I could find some awesome artifact or something, but the things that are fixed are pretty much only plot items (keys to certain areas, etc.).
I do agree that by the time Xeen game around the games were in a totally different league, but it has been a lot of fun to see what the early games were like and learn the common threads that run through the series. I used to think that the games basically had nothing to do with one another, but now I'm realizing that there are certain things that connect them all, which is pretty cool.
By the way, I still had fun with game 6, but I agree that it's not as good as Xeen. There's a bit too much of a monster slog going on in 6, but there's also some fun to be had if you stick with it. There are also some mods for game 6 that make it a little less tedious.

It was definitely an amazing job JVC pulled off, no question about it. I think I've just been spoiled by MM3-5. :-)
I'll have to double-check that...not saying I doubt your word, I just can't remember if I had magic weapons on me or not. That might change my opinion on MM1 being just too much hassle after being spoiled.
I dunno, maybe I'll work my way backwards instead. Finish off Xeen (including Swords of Xeen), then go to 3, 2, and finally 1. Instead of reliving MM's evolution, I'll just de-evolve. ;-)

I can verify that magic weapons hurt Caryatid Guards.

Well I actually didn't use the mods myself, but I've been seeing several posts on these forums about modifications to weapons and enemies to MM6 to make it less of a grind. A quick check shows that you've seen these already (you posted to some of them) so I guess I'm not helping you out too much. Some quick googling shows a mod up on ModDB for the game but I don't know if it's any good; also there's the total conversion that's been mentioned here, entitled the Chaos Conspiracy, but again I haven't tried it myself.
Playing the base game, I found that getting the right spells early on can really help with the grinding, but it's tough when you don't know where they are at first. Outdoors especially, if you have Meteor Shower and/or Starburst (I think it's called Starburst... it's basically like Meteor Shower) it can really help to take out mobs of enemies. I felt kind of stupid when I realized I was grinding out in some tough areas when there were easier areas, WITH spells available for sale, that I hadn't even been to yet. Oh well.
I actually never played MM7, so I can't comment on that relative to MM6. The Xeen games are still my favorites though (although I am only starting MM2 and haven't played MM3 yet).

Righto. Ah well. There's the one mod posted here with the chief purpose of upgrading melee fighters, which I intend to try out next time I play. It should help, but I'll find out once I've given it a try, I guess.

Have you tried this Conversion - The Choas Conspiracy