My biggest hesitation going from the 665 to the XT was giving up the satellite weather. I ride a lot where there is no cell coverage (WV). Unfortunately, the new breed only uses cell. My 665 became unresponsive at times and unpredictable. Still works for the most part, just can't trust it. My 690 came with a 665 mount, so it won't be fully retired. I know Garmin would have sent me a replacement for some fee, but decided to give the XT a shot. Below with weather from the cell phone.
It's very frustrating trying to get the old Basecamp (.gdb) files into the XT. Haven't figured that one out yet. Building a route on the XT is also more of a pain since you can't build it by picking the next waypoint to be near the last one. Only used it on 2 rides, but it looks to be doing a much, much better job of letting you see the smaller roads around you and where they go. That was always a horrible limitation of the 665 and earlier. Zoom out, roads disappear. Now, the road seem to be saying on screen with automatic zooming. Much needed improvement.
Still a ton to learn about this unit, but so far, I'm thinking Garmin finally made a product worth buying.
Oh, and it really is daylight readable for the first time ever.