My $0.02

Modes in general need to have some sort of challenge that is more than "shoot the blinking lights" and you should get progressively more payout the more shots you hit within a particular amount of time. So shoot shot A to get a payout, shoot shot B within X seconds later (hurry up), the payout progresses. Hit all shots within hurry up limits, maximum payout, mode ends, or now go on to Part B of the mode (add a ball multiball for instance), then rinse and repeat until maximum balls in play is reached, then either allow player to complete a sequence to add balls as balls leave the table, or just end mode when balls on table = 1.

This is a very common ruleset implemented across many machines...

Wizard Modes:
These should be some kind of "Last thing you will ever try to achieve on this machine" and be tied into the climax of the theme. Wether it's "fighting the ultimate boss" or facing your arch nemesis, or just completing some sequence that has some meaning for the theme, this should be the ultimate goal of the player/protagonist in the "storyline". Progressive awards for completion of earlier modes is usually some how incorporated into this, by increasing jackpot payouts or awarding bonuses linked to previous achievements. Tying an ulitimate wizard mode to complettion of all previous modes is common too. What is most fun, in my opinion, is having to make a shot during multiball play that requires major concentration on all balls in order to hit it, that is, there is no way to trap up, catch two of 3 balls, and then shoot the super jackpot... this should NOT be some kind of "shoot your way out of a wet paper bag" contest but more focused on direct ball control IN MOTION, that is you need to put several balls in motion to get them out of the way, then while they are, get control of a single ball to shoot the Triple super secret jackpot.

Some machines make this final mode one to be revisited, working up to the final mode again but increasing the difficulty of all modes leading up to that mode.

Objectives:
Pinball has a very limited set of objectives when you look at the mechanics involved. You can shoot for accuracy or sequence, so shoot shot A, then B, then C gives payout. You can shoot for quickness, so Shoot shot A and then shot B within X seconds gives payout. You can shoot for repetition, so shoot shot A, then A, then A, then A gives a payout. Other than shoot shot A, get a payout, that is the list of awardable tasks in pinball. So Sequence, Timing, Repetition, and Accuracy are the key rules you must incorporate into any "mode" you write. So you can see why most wizard modes "feel" very similar, and why most ruleset these days are looking to break out of this by incorporating things like risk/reward, letting you stack jackpots to be collected later after increasing some bonus multiplier, or making you take you hands off the flipper button with the action button, something I find most annoying.