|Seriously.. if your complaint is with having to write stuff down and/or do simple calculations... just open up Excel.|
It's true that excel is sufficient, but a custom program lets you have a better interface, and it's a good opportunity to learn some GUI programming IMO.
I tried making an interactive character sheet 3 times, and every time I got bored in the middle of it because there was too much stuff to consider, and making GUIs is bothersome.
I'd say the minimum features are name, class, level, XP, HP, AC, saves, stats, ability scores, inventory with weight calculation, equipped items, money, class features, spells, talents.
That's all that comes to mind for now. It's basically most of the stuff you can find in a character sheet.