As on many airlines, good and bad - often depending on your Status Level.
I have been Platinum for some time. Comments based on that level:
1. Greatest advantage: Can use award travel for any flight that has a seat for sale, no restrictions! I think this is the only airline with this policy. (includes companion also if traveling with you)
1a. They have a 15,000 mile Award for 750 miles or less travel. A good deal for shorter flights.
2. Free upgrade with any ticket (other than free travel awards) for Plat. with 100 advance request. I get 1st about 90% of time.
3. 24 hour Platinum desk service on toll free number. Rarely on hold for more than 15 seconds.
4. 1,000 mile minimum (count toward Status) and 100% bonus. A 4 leg round trip from KC to ORD through STL will net you 8,000 miles + the miles = cost of ticket. Plus 1,000 mile for WEB booking. About 9,400 miles for that trip.
5. Good bonus programs (although I hate the registration required on some).
6. On time is pretty good, although STL can be a problem if bad weather.
I am unsure of policy, but I have never had any problems being allowed to fly standby on same day with any ticket (discount or free). But, I am low man on list (as expected) so don't always get on.
Downside: Fewer destinations and partners than other major airlines. A bit older planes and terminal areas. Fewer Ambassador Clubs.