Here's the deal with the X5L - you can't generate playlists on the unit. So, if you're into that (makes sense with 20gb of music, actually) that could be a big turnoff.
I also wish it had a wrist strap, just to make absolutely sure I never drop it. My CD player has this, and I would have thought it was absolutely necessasry for such a small, fragile, expensive thing.
One other advantage that the X5L has, although I don't really know how many other players do or do not have this feature, is the way your computer sees it. It shows up as a hard drive, if you don't want to use their software, but the included software is quite lightweight and easy to use. I've also connected it to several digital cameras and transferred files with no problems.
I was disappointed by the stock cans, not because they sounded bad, but because they were not made right. The left earbud had a lenght of cord about 1/3 as long as the right, and the pads were not installed on the earbuds. To this day I haven't figured out how to put them together, but with my ER-4Ps, I don't care that much.
Battery life - well, unless you listen to nothing but 128kbps CBR MP3s, and don't have the screen too bright, you're looking at nowhere near 35hours. I'm estimating mine will last about 19 total hours, but mind you I have a lot of FLACs, and I've watched 2 episodes of Arrested Development on it. I know the battery monitor on LIONs is not accurate, but if this thing goes 35 hours before it dies, I'll be very surprised.
Another thing - the video is excellent for the size of the screen. You won't be reading any subtitles, and faces are hard to make out, but I was honestly blown away at the quality for such as small screen.
Worst problem is the stupid little subpack that you have to use to charge and connect to the usb port on your computer. This is ridiculous and there is no reason I can see that they couldn't have put these ports on the unit. My guess is that it's a cost cutting move. Other than that, the build quality is good, but I wouldn't go testing that by putting it in your pocket uncovered or dropping it any distance. I'm even careful setting it down on the table.
My main regret is not getting the 30gb/not waiting for the 60gb version, but overall it's exceeded my expectations considerably. Maybe that's because I'm so pessimistic, but I love the X5L regardless.