i'll give the same feedback i give every season. the casters need to talk way less and think way more. almost all of them start sentences without thinking about what they're saying, end up with a word salad mess, and usually by the time they've corrected themselves they're 15 seconds behind. remember: we're watching. it's not radio, it's tv. you do not need to painstakingly list every player movement and every kill. and if the observer is doing his job, when you say things that contradict what we're seeing, it just makes the cast dissonant. trust your observer.
watch professional sports broadcasts. notice how they use the downtime (before the pitch or snap, which in tf2 corresponds to during stalemates) to prep viewers for what could happen. they do this quickly and precisely, and it saves them a bunch of talking during the action that follows. remember that you don't have to fill every second of action with words for the sake of words.
(of course, i recognize that they're volunteers and none of this really matters. but just in case they want to improve, or springboard into doing industry casting in another game like sideshow, cornpop, etc. ...tf2 casting has gone downhill, and i think it's because most of the people who liked casting as much as they liked tf2 have left for different games.)
note: i thought the observation was excellent in every invite cast i watched this season. noticeably improved from years past. seemed like the viewers hardly ever missed highlights and often the observers saw offclasses and aggressive plays before the casters did.