Originally I was thinking of this thread only in terms of spells that "ruin" exploration or become "must always prepare/cast" type spells, which as I said, is not an issue in my experience mostly based on my playstyle and current set of players.
But there are things that bother me, like. . .
I am not a fan of at-will cantrips (esp. damaging ones) at all. I don't think they break the game or anything, but aesthetically I think they undermine the "magic" of magic and make it into a repeatable infinite resource like a common sword and more reliable than arrows (which can run out)!
I want to use a spell roll system (kind of like a reverse re-charge ability) that limits cantrips, but you never know what that limit is because it changes day to day. You roll the check every time you cast a cantrip and if you eventually "fail" your check the casting is wasted and you can't try again until after a long rest. You are less likely to cast V
icious Mockery or whatever over and over if this is the case - and you might try to mix it up.
This doesn't happen with higher level spells because they use a finite resource, while a lucky caster might be able to cast cantrip umpteen times if they are lucky and their spellcasting skill bonus is good.
I have not tried to introduce this in my current games yet because I thought about it after we had already started and in one group spamming cantrips is never a problem.
Oh and I'd go back to making some spells not work on certain targets due to Intelligence or whatever. Like vicious mockery should not work on creatures of animal intelligence or maybe aberrations.
I hate anything that makes magic into just another form of technology - as such it should be arcane, unreliable, and expensive whenever possible, not just something that "everyone would have" and thus would fundamentally change the world far more than most D&D settings are changed by magic's existence.
I'd make
Continual Flame a 5th level spell. As it is right now, I have it require 500 gps in ruby dust, not just 50.
Those are personal preferences of course, and I don't necessarily think that D&D has to be that way out of the box because all D&D rules are toolsets to me and the tweaking it is part of the appeal of the game. As I have said elsewhere, I am just not that interested in D&D (or any RPG really) without the DIY aspect.