First, let me say, that I don't consider "change class like underwear" a bad thing, just a style or strategy, that is not for me.
Back in the day, when the forum was "alive", there were many heated debates on the topic, thus my comment ... alas, those staunch defenders of that style, don't seem to haunt the board anymore.
That said, I would be interested to hear your take on how this game is so addictive (as opposed to others, I venture to guess we have played, like Bard's tale, EOB, Star Trails, etc.).
My own opinion on this has changed with time (and perhaps wisdom). I think a large part of it has to do with when you first play the game. If I had never heard of Wizardry 7 and played it for the first time today, I doubt it would have the same impact for me.
Another large part, I think, is the length and breadth of the game. By that I mean the variety of ways you can play it: characters, races, strategies (breadth) ... and the amount of detail in the game: factions, treasures, spells, monsters, locations, puzzles, etc (length).
I also think it was a high quality product, that just stands the test of time. The other thing I didn't realize at the time (I do now after playing MW2), is the constant positive reinforcement ... every couple fights or so, someone levels up, or gets some good loot, or you solve a puzzle, etc. In other words, there is always something good just around the corner (unless it kills you )
Another factor that plays to Wiz 7's favor is coming out when we could become enamored with it more easily ... today, there are so many things to be distracted with ... oops, gotta go, I am up on Words with Friends
Tools for Wizardry(r) 7