Ultimatecalibur
Explorer
Somehow the balance of these items seems way off to me. We're limited to +1 weapons (except for the special ones) to go with the new flat math concept.
On the other hand, melee attackers (but only melee attackers) get a "girdle of make every weapon you might wield including those which already have bonuses at least +4 better than it is now" (assuming a Fighter with STR 20, going to 29).
You do realize that the Belt of Storm Giant Strength is the only artifact currently in the playtest document? And that if you only have tough encounters from level 1 to 10 you might get it if you are lucky by RAW.
I'm also not in favor of the new charges rule on staffs and wands. They are too luck-based in terms of using up your resources and only serve to encourage extra-cautious play instead of making full use of what you have. Most players will simply treat their valuable wands and staves as having appropriately fewer charges, always making sure they stay at 1 (or higher, if the DM rolls the recharge die).
Does every party need to make full use of everything the party has?
You should also consider that some players will risk that 5% chance every time while others will be as careful as you describe and only use that last charge in the most dire of emergencies. Both are valid play styles.
A "burnout" mechanism is a good idea, but what if this just made the item temporarily unusable until you invest a few dozen / hundred GP into a 24-hour ritual?
Because they want to avoid a base assumption of magical item enchantment? What you describe could easily be an optional rule/module.
I believe there's a lot of room for optimizing things - the balance of items and their scaling with level was much better with almost all previous editions.
But they are not trying to scale them to level this time.