I'd like to second multicoin support. It would be amazing if you could choose any coin you want that uses a similar wallet. I know UnbreakableCoin, for example, uses a similar wallet.
The ability to use a "blank" version to add your own CSS.
Code in clearly-labled chunks with tons of comments to make reading and using it easier. I hate when people don't notate their code!
Ability to only have the faucet appear once user completes a task. For example, click and drag an icon, watch the short ad video, get a multiple-choice question correct, or click three links (waiting between clicks) to make the faucet appear.
Have
SweetCaptcha as an alternate captcha to the Google Re:Captcha.
Option to hide the faucet if adblock is on.
Randomized payouts for a "game" feel. Be able to choose how often (in percents) that the user gets each reward. The system adds up and will not let the user save the settings unless all percentages equal 100. For example, the visitor might win 100 (70%), 500 (25%), or 1000 (5%) Satoshis at random.
The option of having a timer between payouts. The timer will show up on the main page when the user visits to let them know when they can get more.
Set minimum withdraw in order to prevent everything from being eaten by fees. Also ability to set minium withdraw limit and a toggle whether the user or the site owner pays sending fees. Users can select a higher withdraw limit if they want.
Ability to "remember" a user's faucet address so they don't have to input it every time.
Option to have users make accounts so they can play on multiple computers. Also encourages loyalty and enables things like being able to send a newsletter to users or have different user tiers with different prizes.
Different user tiers with different prizes. Potential qualifications for higher tiers could be: how often they visit in a day, how high their balance is before they withdraw, how many times they have withdrawn, what country they are from (let's face it: USA ad clicks pay more!), how high their withdraw limit is and if they have chosen to pay from their balance to "upgrade" for a little while.
That's all I can think of off the top of my head.
I hope it helps!