The biggest one for me was being limited to 60i for a frame rate with the XA10. The XA20 lets me record at 60p which is huge. Not only does it let me do it at a bitrate of 35mbps (which when slowed down to 24fps is only a measly 14mbps) like a lot of camcorders that record 60p, but it's one of the few that do a real overcrank. What that means is I choose the bitrate and tell it what speed and the camera records the fully slowed down footage at that bitrate so there's no need to slow it down in editing. I can record 24mbps with the XA20 which gives pretty great results. 24mbps vs. 14 is a whole lot of more info stored in each frame! Compared to the XA10 which only shot at a max of 24mbps (which means only 9.6mbps of info in each frame when slowed down from 60i to 24p) and you can see why I'm excited about it. A lot of my videos use slow-mo so this is awesome!
The other thing is consumer and prosumer cameras all have 4:2:0 color space. Professional cameras have 4:2:2 color space. It's all technical mumbo jumbo, but what it boils down to is its about compression and how that compression stores the color information. So the more compressed the video, the less likely each pixel will be an accurate representation of what you were shooting, but more of an average (and sometimes it's way off with 4:2:0). For the average Joe or Jane it's a non issue but when your trying to do green screen or play with your colors (like I do in my videos) then you start noticing problems because of the color space. The XA10 had 4:2:0 color space and no matter how you output it, it was 4:2:0 color space (which is more compressed). The camera processed the signal to 4:2:0 before outputting anything. That's normal with cameras under $5000. It's the big thing that separated prosumer from professional (4:2:2 color space). The XA20 changes that. Sort of. It still records in 4:2:0 color space using either AVCHD or MP4, but the HDMI output is an unprocessed 4:2:2 signal because Canon listened to consumer feedback. So if I ever needed it, I could pick up a SSD recorder and record a 4:2:2 signal from the XA20. That's not a priority for me right now, but I know 4:2:2 is there if I need it.
The other things that are huge for me are:
There's a whole lot more I like but let's just say that at this point I'm happy with it and it's what I'd hoped for from the XA10.
For the price, I couldn't find anything that beat the feature set this camera offered. Sure it still records in consumer codecs, but with 4:2:2 HDMI out, if I need better, I know I can have better. Truth be told, 9 times out of 10, AVCHD & MP4 at high bitrates look just fine.
Until the time comes that I need a 4K camera, this is the one I'm settling on as my long term camera, no matter what else hits the market. I'd been looking at it for a year and the more I saw, the more I liked.