While I think 4e had far too many magic items (and a whole bunch of them terrible with others being very powerful), I think I prefer 3.0's magic item (3.5 with it's keen, brillaint energy mercurial greatswords with improved critical feat, dual-wielded through monkey grip) system in the sense that it was versatile, but it did definitely allow for the creation of some very broken magic items (especially the crafting rules in the dmg), but 3.0 also had a lot of abilities built into the classes as well, and still had a lot of magic items to boot, and mundane items that came with enhancement bonus (adamantine weapons and armor for instance) inherently that worked even in anti-magic areas, so it was also a pretty flawed system. I want a happy medium between 3.0 style customizable magic items and 5e's no magic items necessary design. I've said it before (before the crash) that I think a 3rd style system where certain effects carry an equivalent enhancement bonus value, and items can only have so much bonus on them. Honestly, I miss the huge variety of wondrous items and rings and all that jazz that the 5e dmg just didn't include. I'd like the introduction of more non-combat items, stuff to augment exploration and role-play, with the introduction of a customizing system for weapons and armor (so for instance, you could get a +1 flaming greatsword of speed, or a +2 Glaive of Warning, or a +3 bow, or a suit of +2 Mithral Plate Mail, or a +1 Mithral Mariner's Plate Mail, or +3 Studded Leather, and then like a mask that grants expertise in performance, or gloves that give an effect similar to mage hand legerdemain, or chalk that lets you draw a door to Mordenkainen's Magnificent Mansion on any vertical surface, or an amulet that lets you mimic voices. Just more flavor options that have rarities listed that are actually in-line with other magic items (since it's not exactly transparent how such non-combat items would be graded).
I didn't really find in the early days of 3rd (didn't own any of the books, so I just worked with what was given) that I felt my character needed magic items to accomplish tasks that were appropriate to party level, I did find that they let you pull off things well beyond level though (especially items that granted bonuses to skills). In 3.5 though I find magic items to be less important since you could MC to get similar effects that actually scaled as your character improved (I don't think pun-pun required any magic items to pull off, the infini-bard did though). In 5e, when I'm making builds, I don't even consider magic items until after the build it done and I'm looking at ways to cover the shortcomings (usually revolves around amulets of health and cloaks/rings of protection), which is nice. I just wish there was a better selection of item options because the current selection favors trope-y play (the longsword tank, the longbow archer, gauntlets and belts of strength, and ioun stones floating around everyone's heads) and it's just kind of boring when rolling up treasure to be like, "Ok, well, you've found a +2 longsword, that's better than what you have right? Oh, it's not? Well, more GP I suppose..."
With 4th edition, I mean, come on, it's part of creating a character above 1st level that you start with 3 free magic items, plus gold to buy more. I'd say that's a pretty strong indication of the level of magic that 4th edition ran with. Seems to me like a no/low magic campaign wasn't even really a consideration in that edition, what with the heavily math-dependent monster design.
5th has, I think, the right balance regarding magic item power level, I just wish there was a wider selection that was appropriately graded so there was a better idea of when it would be appropriate to introduce a ring of the acrobat (hypothetical item grants expertise to acrobatics checks, has some combat implications, but I don't think they'd be particularly potent) or an amulet of alertness (expertise perception). Like, are they rare, very rare, uncommon?
I just feel the magic item creation guidelines are not particularly clear or useful when it comes to saying "this type of feature is worth this" whereas in 3rd edition it was formulaic, yes, but that was a solid and reliable way to measure the potency of various effects (before restriction discounts) so you'd know "Hey, this item I made for your characters specs out to a 2400 gold magic item, it'd be reasonable for me to distribute that in loot around level 6+ so I'll give it as treasure in this encounter."
Also, not a fan of the rarity price-range system, I'd like an actual gold value to better refine what end of rare particular items were, especially since you can easily adjust prices dependent on setting (high-magic worlds keep stock price, low magic worlds double the price, no magic worlds have no magic and so are unavailable). I do, however, like the buying and selling magic items section (I suppose the rarity range could be representative of the possible range of price based on results from buying/selling rolls, but what's the actual base starting point, the middle of the range, the low end, the high end, what?).
5e's homebrew friendly, DM-ruling-centric design, I think, hurts it in regards to keeping your custom content balanced to the rest of the game's design. With rules as is, how does one determine if an item is going to be too powerful compared to other level appropriate items (assuming you follow the character wealth above 1st table at least roughly) without putting it into play?
When I played 2nd edition, people had all sorts of magic items all the time, staves, wands, rings, potions, swords, bows, ammo, ropes, etc., and that's one of the most common editions people point to as their favorite, and the few novels I've read, practically all the important characters were completely decked out in magic items and were chasing down world-sundering items as a viable career choice (like there were enough of such items that one could become a professional and have enough work to last you your entire life and still have items left unfound), which makes me think of 3rd and 4th edition characters that oozed magic.
Also, real fast, in a world with actual magic item shops, without a bajillion golems running about and all magic item merchants being high level wizards and clerics, what's to stop thieves from just robbing all the items? Sneak into the shop, snag a few bags of holding, and just start dumping items into the bags. Why wouldn't a mundane merchant run a magic item shop? If they hire guards to guard the place, you still have to have a place that's actually defensible, are all magic item shops old wizard towers or small keeps? I don't like the idea of shops where you just go in and say, "Yeah, Jim, I'm looking for a Scimitar of Speed, can you help me out?" and they come back with "Oh yeah Bob, just got in an order of those, that'll be just a stack of gold larger than you can carry!" I like the idea of having to find a merchant who might be in contact with someone who knows a guy who possibly has something you're looking for and who maybe, just maybe, would be willing to part with it for 120% of market value. You can still buy items if you're looking for something specific, you just need to jump through some hoops in your downtime, otherwise you can do like everyone else and kill dragons and hope it has something you're looking for in its hoard. Obviously I exclude potions from this (the rarer the potion, the more remote the crazy hermit who "sells" them, and by sell I mean will let you purchase them after sending your group on a quest to find exotic ingredients for some other potion) since alchemy is a pretty common thing from what I gather (in most worlds at least).
Yes, I know, not everyone likes the idea of a system similar to 3rds regarding custom magic items, I understand that 3rd borked it up with the +10 enhancement limit and the huge variety of powers that drastically changed the behavior or weapons in combat (brilliant energy bypassing armor and natural armor really changed a lot of fights just as one example), but in 5th I think it could very easily be toned down and the range of effects rather limited (your basic elementals, speed, bane, animated, keen, throwing, returning, special materials (which didn't count towards enhancement bonus and which also carried enhancement bonus inherently like adamantine, which could get you good effects cheaper since you could get a +2 adamantine greatsword then enchant it with stuff but only pay for a +1, then use the +2 inherent from the material for att/dam), etc.) which would help to keep players from acquiring abilities that combined to throw off combat balance (improved crit with keen on an increased threat range weapon made for some stupid crit chance and that's not even all the way to expand crit range, nevermind things like vorpal or brilliant energy), but still let them have options aside from the decades old trope weapons that everyone always goes for. I swear there's a section that does talk about an items bonus shouldn't exceed +X, but that's not particularly helpful outside of creating legendary and artifact tier items, which doesn't help for the vast majority of play. I mean, regardless of how pro-powerful characters I am, I still think it's absurd to have a level 8 character running around with an artifact item (unless it's a story item that they can't use because it requires attunement by a good aligned red dragon divine spellcaster), which is why I feel the DMG section on making magic items is, for all intents and purposes, useless.