Everything. Researching is horrible. Purchase flows suck. Fees suck.
Portfolio analysis terrible – For example on a stocks page there isn't even an easy way to see existing positions, let alone my historical purchases like when, how much and what price. It's just "here's this stocks history" not "here's this stocks history including YOU'RE history with this stock.
And on and on like that.
I'm just sick of using software that feels like it stopped improving 5-10 years ago....and figured that has to be more out there.