I've had experience with many iterations of the RTI from the first gen in the HS, 3RX, RCF, IS, NX, and 4RX.
Only one form factor works with relative ease, control, and precision, and that's the touch screen version with force feedback disabled. It's a fairly natural way to move the cursor and select it with good precision unlike the mouse controller where I still overshoot my selection one in ever four or five times.
With that said, thank goodness the new LS and LC have the touchpad version.
As for software, I guess I'm one of the few that likes it enough, better than the '17 A4's interface in my opinion and one of the things I disliked about the A4.
POINTING HARDWARE
Both Remote touch mouse and touchpad are good premises. Problem is in actual realization. When the car is standstill everything works just fine but once the road distortion comes into equation everything falls apart. Actual feedback on the controller has to be self adjusting to driving circumstances, it has to become tighter and tougher in feedback/movement. In my opinion the mouse has to have some sort of electromagnetic mechanism in order to achieve that. When road becomes very bumpy controller gets more crude to the hand movement, when car is bumper to bumper in traffic controller get relaxed. With touchpad it would be even easier for them to achieve such effect cause its all software
INFORMATON ARCHITECTURE & INTERACTION
Available information and interaction on screen is too detailed and there is too much possibility on screen at once, great for standstill very poor when drivign. I am aware they tried to minimize screen switching by introducing the split screen but its the split screen that makes all the havoc. There is no clear physical distinction where is the border between two windows, just like that you can be all over the place when in fact you just want to fiddle with navigation (Navigation screen button hunting like full screen map is atrocious decision but its whole another story). In my opinion narrow screen on the right should have dedicated hardware controls assigned to it. Basically there should be a small pad with hardware keys on the right side of the touchpad that always correspond to small screen. Make it a 12 button layout like the phone dial but have each key adjust its function according to the screen. In AC small screen number 7 is Driver temperature up, number 4 is Driver temperature down, number 1 is Auto AC. All of you who have numpad on your keyboard right now would know exactly what am I referring to. Also there is no need for free floating display cursor to be show on non-map screens, it should stick to buttons only.
GUI
General graphics elements and arrangement of the icons and options on screen is quite poor, lots of submenus for no obvious reasons and lots of vertical scrolling instead of horizontal scrolling to take advantage of the wide screen. Huge graphic headers that do nothing really limit the amount of space available for the vertical scrolling, in media screen you have available only 5 items at the time. Without the header it could have easily been six at least and if horizontal scrolling was implemented instead of vertical they could have stacked 12 songs/items on one screen. I could pick apart GUI until tomorrow but overall it suffers from some basic fails. Navigation has no clear distinction of what's an actual button on screen and what's information such as compass, altitude, etc. When in music screen what is the first thing you want to do? Have access to Play, Mute, Skip that is the top priority but on Lexus music screen every command like shuffle and repeat has equal priority as basic controls. It gets even worse, when you click/tap to play the song (which unnecessarily brings up song dedicated screen) default selected option/button on screen is Album Image instead of PLAY button. This means you have to scroll to the Play controls on the left of the screen. Someone did not think this through. Solution is simple dedicated audio knob like in Audis which controls volume and skips or just use audio controls on the dashboard instead. Drawback of using Lexus audio controls stacked on vertical dash is the hand travel, you have to lift your hand of remote touch, apply desired controls and lay back your palm on the mouse which means you have to have quite good body mechanics memory in order to continue using without having to look at the screen to remind yourself where you at. Since Lexus mouse/touchpad is multi-axis control, unlike Audi knobs which are only single axis, there is some a bit more complex brain to muscle coordination going on. Overall GUI on this thing is designed to be touchscreen operated and most of the shortcoming come from this premise.
SCROLLING HARDWARE
This is something I wish Lexus has implemented. Instead of having up and down hardware keys in the middle of Map and Menu buttons maybe better option would have been a dial disk for scrolling purposes on the side of the remote where the redundant enter button is located right now. That would be a lot more convenient as your thumb would always rest there. More advanced approach would be 360 scroll ball which would scroll only in available directions on screen but it would make a lot difference when using the Map. Inside Navigation scrollball would run the cursor all over the map while the touchpad would select only the buttons on Map screen, this way your hand doesn't need to go all over the map only so it could reach a certain control. If you want to zoom in or zoom out of the map just push the ball and rotate it in one direction to zoom or opposite to zoom out. Like I said this is more advanced approach.
On contrary good thing about Lexus infotainment is the amount of vehicle customization and customization of the infotainment itself. In this dedicated area Lexus has to be among top 3 manufacturers to ever offer this.