[Motorola Droid 4] Septfox:
Cleared some room for a ROM slot and installed out of curiosity. Seems to run pretty well, a bit choppy on occasion, but...much better than I expected, to be honest. As far as UI smoothness goes, it does mostly feel like an upgrade; on the other hand, actual speed of starting apps seems slower in some cases, as well as occasional (what I would consider) excessive delays when waiting for an app to do something intensive. I should probably take some notes on what and where...

I'm not sure if these all belong here as opposed to an official CM thread somewhere, but some (admittedly minor in the grand scheme of things) problems I noticed while messing around:

AOSP keyboard gestures aren't working when enabled

Onscreen keyboard isn't dismissed when the physical keyboard is opened, and still pops up if a text field is selected while the keyboard is open (though it can be dismissed manually and the text field will remain selected)

Accessibility options for display stuff (color correction, inverted mode) aren't working (lack of driver support?)

Turning on music track switching for volume button holds will block or disregard volume changes while the screen is off. Disabling the option causes volume control to work properly

When volume wake is enabled, and a volume button is used to wake, the keypress "sticks". This causes a track skip if the above option is enabled

Volume wake doesn't work while the CPU is sleeping (though iirc, this was a problem in previous CM and Slim versions as well, a hardware limitation?)

I'm not sure if it's because the media service is quietly crashing, or something else is going on, but music playback randomly stops while using the CM player. Poweramp doesn't seem to be affected nearly as much, but it did also stop once while I was installing something

Wifi seems very slightly flaky. It's dropped the connection a couple of times, and refused to find the AP and pick it back up for several minutes

I know, I don't have a logcat to post for those last two. I'll get one dumped the next time I play around with it.

Other thoughts:

Idle battery life seems decent. It looks like the various Google services are a bit less prone to keeping the phone awake these days, so that's kind of nice. Without needing to manually go in and kill/disable anything, I was seeing around 96/97% asleep when letting it sit for an hour or two. I'll let the phone idle overnight tonight to get more of an idea of the idle draw, expecting around 1.5%/hr at most. As a reference point, Slimkat is capable of 0.4%-0.8%/hr (or less, I'm rural so the radio is always blasting at full power) with all the Google wakes disabled, data off and Wifi half on.

The phone wakes nearly instantly when the keyboard is cracked open, whereas KitKat keeps the screen blocked/unlit for several seconds (or, always has for me, anyway). Less waiting for a usable state for us unfortunates who have dead or defective power button circuitry.

We don't have a gyro sensor for ambient display to use as intended...but we do have an accelerometer that can deliver similar information. I don't in any way mean to imply that it's as simple as "switching it over", or that it should take priority anytime soon (if ever), it's just a thought.

Overall, it's a very solid start. I look forward to seeing how it progresses.