1. Support for arbitrary-precision arithmetic. The Nspire family of calculators have this, and it makes them tremendously powerful. I also have an Nspire, and it is a tough decision for me to choose between the two calculators I own because while the Prizm has many advantages over the Nspire, the Prizm cannot perform operations involving very large numbers (say, 23200)
2. Showing what each function in the catalog takes in. When I use the catalog to select a function, I often don't know what inputs I should type in, or the order that they go in. This can become quite frustrating because I would then have to experiment with the function to see how to use it. Reserving a line in the catalog menu to display what inputs a function needs and the order they go in would be very useful.
3. A better font. You might think this is a minor complaint, but the font of a calculator contributes tremendously to the look and feel one gets when using it. I believe the font is too thick (it looks like everything is in bold), and also too large in most places. It also has serifs, which makes the calculator look a bit outdated, and characters such as the lower case "p" don't line up with the rest of the characters. Changing the font to something that is sans-serif and fixes the problems I mentioned would improve the look and feel of the Prizm significantly.
4. Fix the logarithm button. This is only a minor complaint, but pressing the logarithm button will give a log function that doesn't display what base it is in. However, if you go to the math menu, and then logab, you get to specify the base as well, which I prefer.
5. Allow third-party C and assembly development. Not doing so has been TI's greatest mistake, and it is one that you can take advantage of. Allowing third-party development will attract a large audience of programmers to buy the Prizm because they are tired of jumping through so many hoops to develop on the Nspire. The programs they will make will also benefit Casio - believe it or not, many of the programs made for calculators aren't games, but rather extremely powerful utilities that extend the capabilities of the calculator even further! Just look at what TI-84 developers have done over time: they made extremely fast prime factoring programs, added support for arbitrary-precision arithmetic, added the ability to type lowercase letters, and even allowed the calculator to recover from RAM clears! Opening the Prizm to third-party development will make the Prizm even more powerful, and it would be much easier for Casio to release an SDK than it would be to program all the features third-party developers would have added.

Implementing these suggestions, which can be done just through a software update, would make the Prizm a near perfect calculator, and it would be an easy choice for me, as well as others, to pick between this and an Nspire. I truly hope that Casio will listen to these suggestions.

Thanks for your feedback and detailed suggestions.  I'm glad you are enjoying your Prizm and I hope you share the word with other students and teachers; word of mouth is the best way to spread the news.
 
I will certainly pass your suggestions on to those that make the decisions, but wanted to take a minute to respond to a few of your points:
 
1. Arbitrary-precision arithmetic: I admit I'm not familiar with this, but you've piqued my interest.  I will be looking into it.
 
2. Catalog Help: An absolutely fabulous idea -- I don't make these decisions, but I'm going to push for this one.
 
4. The logarithm button: Have you tried the MATH soft-menu in Run-Matrix?  I think this is the button you're speaking about.  From Run-Matrix, just press F4, then F2 and you'll get the log-of-any-base template.
 
5. Third Party C Development: From a certain perspective, I'm totally with you.  I've got some programming background and I've seen what a nice community of modders there is out there.  And it certainly would, as you said, open up our calculator to a great deal of demand.  However...  we're a primarily a provider of calculators to the education market.  Can you imagine how teachers would react if calculators could be modified?  You and I both know that modifications would include things like faking a memory reset or other things that would facilitate cheating.  Until we figure out a way to allow modding AND keep calculators safe for testing purposes, we're at an impasse.

Cool. I hope they go for the catalog help. It gets a bit confusing.