Apple CEO Tim Cook and design king Jony Ive have passed their first test. The Apple Watch, apparently designed fresh after the death of Apple co-founder Steve Jobs, is a respectable piece of work. Maybe a hard sell to customers, but the work is indeed Steve-quality. Not “insanely great,” but nothing to be ashamed of.

Yes, Apple without Steve can still innovate. Easy to say now, but I remember a lot of wondering at the time of Jobs’ passing.

Cook and Ive face tough challenges. The future is more theirs to lose than to win. Is there an iPhone replacement in Apple’s future? Not an obvious one, even as the iPhone’s star begins to dim. Are Apple’s best years now receding into the past? They are if the company can’t ignite an iPhone successor in terms of sales and profits.

And that is a very tall order. Here are some of the challenges Apple faces:

1. They can’t “lose” the iPhone — With every iteration there becomes less reason to buy an iPhone or, more specifically, immediately replace an old one. Maybe global markets can grow, maybe the watch will sell some phones. Going forward, iPhones promise to be tougher to sell and less unique than in the past.

The competitors are getting much better and the iPhone seems a tad less defensible in the marketplace.

2. They’ve got to make the Apple Watch into a big deal — If the Apple Watch becomes a fashion/status symbol, those hugely expensive band upgrades will drive revenue and profits. The watch is as much fashion accessory as an iPhone add-on, so it will be interesting to see how the market evolves.

I think the watch will do better than many people suppose. Yet, unlike the iPhone, where the fact that all your friends have one is a reason to get one yourself, the watch may experience a different dynamic. It’s easy to make a case that the Apple Watch is ridiculously overpriced. Friends don’t laugh at iPhones. They may laugh a what your Apple Apple Watch cost. And it’s always there for everyone to see, unlike your phone.

Watches could become important reasons to chose a phone platform. That could be good or bad for any vendor, but if Android has dozens of different watches and Apple has just 38 varieties of a single watch, there could be trouble for Apple.

3. They have to replace the iPhone and iPad business over time — But with what? Television? Cars? Robots? If you believe the future is obvious, please share with us. Apple will need a truly huge “next big thing” to not falter. Thankfully, they may have a decade to come up with something.

4. I believe there is a place for Mac hardware and look forward to buying more — I don’t have strong ideas about what happens here. I just don’t believe PCs are as dead as many seem to think.

It’s true that Steve Jobs returned to Apple at its darkest moment and had to rely on Bill Gates to bankroll Apple’s revival. But once Steve latched onto the iPhone, the company soared without too much difficulty. The power of the truly great idea.

Right now, Cook and Ive have shown they can manage to execute a pretty good idea. Call it Insanely Good, even. Whether insane greatness continues to elude them will become the story of Apple in the post-Steve world.