I installed NTA 4.0 RC 2 over the weekend, then installed RC 3 earlier today. I feel like the interface has definitely become more response, so I'm quite happy with that.
Both times I've installed the update the website restart hasn't completed in time, so the configuration wizard errors and tells me to manually restart it. Manually restarting the website works fine, but thought I'd mention the issue.
It also seems like I've lost my ToS summary page -- the 'Top 10 Types of Service' resource shows no data. If I drill down into a specific interface though, I can see the ToS being recorded. So for some reason this isn't feeding back into the Top 10 resource.
The issue should be fixed in RC4, give it a try :-)