The good: content is fantastic, solid info, great visuals. Useful Wolfram Alpha integration for element specifics. Nice search function, beautiful rotating pictures of elements and items containing them. Nice intro song. The info, I find, is not only i interesting and useful, but also as relevant to our daily lives as possible. Under Bismuth, for example, there is a rotatable bottle of Pepto-Bismol, containing Bismuth Subsalicytate - the active ingredient that is part of the products name.
The bad: steep price, large file. Interface is merely satisfactory, and although there was clearly a lot of work put into this app, there remains much to be desired. Although the rotating pictures are beautiful, they are mostly superfluous, an in my mind contribute little towards what should be the purpose of the app - teaching people about the elements. The writing is solid, but I feel theres some left to be desired, as some of the writing seems to be filler.
Suggestions: what about some options? For example, to label the periods/groups? What about zoom capabilities, because the interface is rather static? Other diaplay options would be nice. Also, and this is rather important - you should be able to listen to music while in the app. It is rather frustrating; I would use the app far more often if I could have some music in the background. I doubt Im alone in this view.
Verdict: do I regret paying the $13.99? Of course not. I would buy it again. There are many apps I have bought that I wish I hadnt - this is definitely not one of them. Yet, there are definitely some improvements that I would like to see. Despite the problems I pointed out, I still think its a great app, and fills an important niche in the app store. I wouldnt heaitate to buy it if you have any interest in the elements or to learn about the building blocks of our universe.