While I don't think that all artifacts should be created equal, and am even happy with some worthless ones (like the black tome) kicking around, I don't think it should be possible to receive worthless artifacts as crowning gifts. Crowning is an important point in the game, and having the let-down of a worthless artifact really sucks the life out of a character. The three that I'm thinking of are:

The Silver Key
Thunderstroke
True Aim

There are a few others (eg, Black Thumb, Bugbiter) which aren't exactly inspiring, but the three that I mentioned are the only ones that I consider completely worthless. These three items should either be removed as possible croning gifts and replaced with other options or improved. Personally, I favour the latter option, and would suggest improvements along the following lines:

The Silver Key -- Being able to better deal with locked and trapped doors is never going to be exciting, so how about giving this artifact some stat bonuses and/or intrinsics when wielded in the tool slot? They'd have to be pretty strong bonuses to be more attactive than the elemental orbs, but would be useful before the water temple and after D48 regardless. Maybe something like Dx +6, Sp +4, grants lucky, grants see invisible.

Thunderstroke ad True Aim -- These have always been eclipsed by ammo of foo slaying, and with missile prefixes and suffixes are now even worse. I'd like to see magical effects added to these two artifact missiles so that you know you're only going to get one shot with them, but you also know it's going to be a good one. In keeping with the names, I'd give True Aim the unerring property (never misses) and make it have a higher critical hit percentage. For thunderstroke, I'd make it ignore PV and have the chance to stun enemies that ammo of thunder has. (If these then proved too powerful, the raw damage numbers could be tuned down a little.)