I'm coming from a Nexus 4 to a Moto X. Here are the things I miss so far:
1. Wireless Charging (Qi)-- one of my FAVORITE features (of all time). I consider this a must-have and was very sad and annoyed that the MX didn't include this feature.
2. Premium Feel-- I've never had a single problem with the glass back and ABSOLUTELY LOVE the way it feels in my hand. Also the curved screen feels amazing too.
3. Notification Light-- I used LightFlow and had different lights for different notifications, even for different people. I wish the MX had a Notification Light combined with Active Notifications so that I could have the best of both worlds.
4. Huge development community/support-- though the MX is getting community it's not at the levels the N4 is (even at the same release time), currently. Hoping this will change shortly.
And the Moto X has some nice improvements/features over the Nexus 4:
1. Screen-- the MX's screen is leaps and bounds better than the N4's. The N4 looks so washed out and crappy compared to the MX, wow, it's shocking.
2. Phone Call Quality-- WAY BETTER call quality than the N4.
3. Speaker-- much louder, better sounding speakers than the N4. No fear of laying the phone down and sound being completely muffled like the N4.
4. Active Notifications-- it's really nice & I think ALL phones from here on out should have it.
5. LTE-- if you live in the US then you'll want LTE even if you're currently not in an LTE market. (It helps futureproof your purchase and when LTE does go live you don't have to buy a new phone!)
6. Motorola Assist-- very handy feature that I use every day.
7. Motorola Connect-- seeing and replying to texts right from your computer and seeing caller ID without the need for a 3rd party app is amazing.
8. Motorola Migrate-- every phone should have this! Makes switching phones easy as pie!
9. Motorola Skip-- YMMV but I think this is a great option if you have to lock and unlock your phone multiple times a day.
And last, but not least...
10. TOUCHLESS CONTROLS-- Even with the screen off you can still use Google Now to control your phone and answer questions. Love it!