It might help feature discovery if the "Manage Levels" screen had a third tab beside Class Features and Spells: "Extras" for druids, characters with Find Familiar or other summoning spells, etc. I didn't even know what the extras section was for and now it's so convenient.

Also, when you level up and the class feature has a selection notification blue thingy, it would be good to put that on the Spells tab too for spellcasters. I leveled up 30 odd caster levels on different characters combined before even noticing it was on the screen... I always went back to the main sheet and used Manage Spells. (Another option would be to make the tabs more noticeable instead of as uncover arrows. 

For races that gain racial features as they level like Aasimar at 3rd, or improving breath dice on Dragonborn, it would also be nice to have a little indicator as you level. Right now I always go back to the sheet and open the features tab first thing to make sure I didn't forget that I got something important.

Thanks for everything! This website rocks.

The builder is planned to be changed/removed so some of these suggestions will be moot (like make spells more noticeable or adding extras).

Draw more attention to new or improved features after leveling up is a good one though.