'Tradeskill' engines don't really reward creativity. With some minor exceptions here and there, they all follow the model of:

(combine X Y Z) -> ItemXYZ, where X, Y, and Z are constants and ItemXYZ is an element in a (relatively small) finite set of predetermined items.

Instead of adventuring to obtain ItemXYZ, you adventure to obtain X, Y, and Z component pieces that you combine to get ItemXYZ, assuming you have enough skill. It feels sort of silly that way. The actual artisan, the guy who combines X, Y, and Z to get ItemXYZ, is not really creative. All he's doing is following a predetermined recipe and applying the skill he got by doing hundreds of mindless combines.

Blizzard's answer to this problem was to shift the focus from item creation to collecting ingredients. They made sure it was fun to gather X, Y, and Z, without just making X, Y, and Z exclusively monster loot. Compared to some other games, WoW's engine was also simpler. Blizzard's solution worked, but only because they sidestepped the core problem.

Tradeskilling appeals to people because it's a creative activity. Players want to be able to feel pride in the stuff they can make. The result is disappointing. Imagination picks up the slack, the novelty wears off after a few hundred clicks, and unless you're addicted to gaining the next level; you aren't going to bother. The way it works now, it winds up only really appealing to people who enjoy organizing things.

From what I've read, Second Life is the opposite. Gamers don't like Second Life, because there's no consistent, professionally-crafted fantasy world to give meaning to anything. It's completely open-ended, allowing for lots of creativity, but what's the point? Obviously plenty of people find a point to SL, I'm just saying this what the typical WoW or EQ or FFXI or DAoC player thinks when they see second life.

I've only heard of two other games with interesting tradeskill engines. I wasn't able to play either of them, so I don't know how similar they are to what I'm going for. One was Horizons, which tanked almost immediately; the other was Star Wars Galaxies, which suffered from being inappropriate for the mainstream Star Wars audience. I say 'suffered' because even though the game was actually doing quite well, it never came near its potential given the franchise name. But whatever the reason, the game was overhauled and the original SWG is no longer available.

So what's the solution?

(ah, this article describes Horizons' system: http://rpgvault.ign.com/articles/378/378346p1.html )

That sounds pretty close to what I'm going for, actually. The solution is, of course, to define a set of building blocks that is orthogonal but easy to use, so that clever artisans will be able to combine in many different ways. (like the 25 different blades, with 25 different handles, etc from the article). My ideas are a little different, but mostly in the details and what sort of controls I'm hoping to give the artisans.