Very slow and unresponsive
After initial page load, clicking between several different email threads can take up to 10 seconds (UI locks up completely, no hover state shown for other threads on mouseover, etc).
It even locked up so bad chrome showed me the "aw snap" page (maybe it ran out of memory, maybe it hit the CPU too hard and locked up, not sure).
Sometimes if I give the page a bit of time to settle after loading it returns to a fluid behavior. But it is definitely a regression from the old OWA in terms of "once the page loads and shows me threads, I should be able to click around without waiting".
This is the main focus of the team right now and we are actively working on improving this.
Diana Mohan Babu commented
The new UI often freezes and is slow on safari and chrome on the mac