I like that it has all the necessary functions to be an online broker in one place - from account opening/closing right through post-trade processes (e.g., reporting) and settlement services.
It's also very good at what you'd expect with that kind of solution -- quick response time when questions come up; clear explanations about how things work or don't work as expected. The UI could use some improvement still but they're working hard there! They've been able to streamline my compliance requirements by automating our back office systems so we can focus more energy towards client service instead of paperwork.