I recall it being slow, with frequent downtime, poor mardown support, and having very poor (or nonexistent? can’t remember exactly) first party non-web clients. I vaguely recall some third party apps picking up the slack (pun!), but integration was pretty basic (they did their best).
It basically stagnated like it was abandon, and then hipchat (atlassian bought and killed it) and later slack just ate its lunch.
