DND_Reborn
The High Aldwin
(bold added)I think a question for any kind of caster rule change is how different you want magic-user tropes to look within in the setting. Rolling back slots and spells available means that casters still feel like casters, just less capable. Depending on the players, that can easily be a good thing or a bad thing.
I wasn't out to change the feel of casters, just nip their power-level or capability to bring it more in line with martials and to have spells be less prevalent in the game. For our group, it is a good thing.

Not a bad goal either, just not what I was going after.Personally, if the DM is going to make changes, I'd rather them make qualitative changes, so that my options feel different in play; not an option I had previously but that they've chosen to make weaker.
(bold added)That's why I like rules changes like using warlock as the only caster, or changing spell lists around (remember that?), or only using sidekick classes. Lowering power levels feels better if it's in the service of providing an entirely different experience than baseline D&D.
Many posters seem to like the Warlock as casters-template. To me it seem too restricted, but that is but my preference. And I've toyed around with running a game with JUST sidekick classes for the PCs, and my group wouldn't mind trying it to see out it goes, but we haven't gotten around to it yet.
As for the bolded part, Heck YES! You should see our spell lists for our games now, only about 35% of the spells have overlap (so reducing sameyness) and spells over 5th level are completely unique in who gets which spell.