I can't say there was anything I didn't like about the convention center, but I can't say that it's better or worse than any of the others I've seen on the Strip. 4 stars seems about right.
Things I like:
1) Convenient location within the Casino.
2) Lots of desks to check-in! (I've seen some where there are only two people available to check people into a huge conference - this one had about 10 staff members checking people in).
3) They took care of my special dietary needs and were super helpful about it as well. I went there for Sage Summit just last week, and it was great. So, I know that the Sage Summit staff can share the credit on this, but the Mandalay Bay staff were also involved in making sure that my food didn't kill me (food allergies).
4) Coffee was DELICIOUS!
What I didn't like:
1) WiFi could've been more reliable. That was frustrating, especially at a professional conference for business people. The Sage Summit had their own Wifi that wasn't much better, but the Mandalay Bay Convention Center Wifi wasn't fast either.
2) The coffee carts kept disappearing. Keep those things around 24-7! People need their caffeine!