Large Variety of terrain, lots of moguls - if you're into that
Flat areas on beginner terrain, lack of good tree skiing
I found A-basin generally disappointing. I'm and intermediate/advanced snowboarder and I found several issues.
1. It seemed like any terrain over 30 degree pitch was moguls
2. The vast majority of tree skiing was on extremely steep terrain, and much of it was roped off.
3. My beginner girlfriend had to unclip and walk on many of the green run's flat or uphill areas, which I don't think you should find on beginner terrain.
Maybe the day I went was just an exception, but there was at least one child under ten for every adult, which I found worrying while I was trying to enjoy my time on the slopes.
On the plus side, we had some fantastic food in the mid-mountain lodge, including a "bacon-infused" Bloody Mary that I HIGHLY recommend.
If you like moguls, you will like Arapahoe. If you don't, there might be better resorts in the area for your money.