MM6 was the best to my mind, but I liked the comparative freedom and ability to grow any character. MM7's light/dark and human/elf (IIRC) decision points offered some replayability, but MM7 began the path of tightening down on what each class could learn. MM8 has the interesting tidbit of being able to have dragons in your party, but that completely destroys any chance of balance - basically, because it is possible to have a party consisting of one cleric and four dragons who let the party fly for free and have unlimited dragon breath as their standard free attack, the mid to late game mobs have to be huge and mostly impenetrable. I can't imagine trying to get through them without the dragons.
I really enjoyed the first "level" (which was also the demo). But I loathed the second level because the difficulty jumped crazily. And I had that problem through the whole game -- a few levels that were enjoyable surrounded by multiple death march slogs. It was a little more interesting to me because I'd never played any of the other Wizardry games, so the setting and the oddball character types and settings kept me going. But it was right on the ragged edge. At least it was less weird-coz-it's-funny than Wiz7 was... I tried to go back to Wiz7 after that, and when the Dallas Cowboy Cheerleader on a rocket cycle came down to give me a quest hook, I decided I couldn't go there...
I'd forgotten about MM10... Given how astoundingly disappointed I was by MM9, I'm not sure that it being by someone other than NWC would bother me. But my patience for "step into room, grind through 100 bad guys, open door, repeat" is much lower than it used to be, so I dunno... Oh, and I refuse Steam on principle (I want to own my copy of the game, not lease it, because I play games for >20 years, durnit!), so that got in my way, too... Glad to hear something about it, though!