After going through several Lunatic playthroughs and recently completing my second Lunatic+ playthrough, I have found that Lunatic offers a much more enjoyable, less frustrating and less RNG-based experience than Lunatic+. With Lunatic, I did not find myself having to reset a map just to roll favorable enemy skills and minimize the amount of Luna+/Hawkeye/dreaded Counter.
Seriously, COUNTER. That skill alone counts for over half my frustration when playing Lunatic+. If the enemy has too many units with Counter, it's gg before you're even out of the preparation phase (at least early on before Second Seals become available). Chapter 3 took a ton of resets because of the emergence of counter before the ability to renown a second seal/use spotpass shops. But it doesn't even match up to Chapter 2, which I think wins the most frustrating level to play in the whole game. On Lunatic it just requires smart positioning and maybe a bit of RNG, but on Lunatic+ you'll be constantly rebooting the map to find a matchup you could possibly win - and even then it takes a whole lot of RNG to survive the first wave without casualties. The design for Lunatic+ is inherently flawed - broken skill distribution makes for an experience which is not very fun and requires unsatisfying tactics/gimmicks to use.
If you're like me, the first 11 or so chapters of Lunatic+ will find you either abusing a Nosferatu-wielding MU paired with Chrom to scape by or DLC/spotpass abuse so that the game is more grinding then it is actual gameplay - and both of these are not very rewarding. Once you get to the Valm arc, the "rescue train" gimmick becomes available - simply rescuing a chain of units to bypass the whole opponent and one-shot the boss in one turn before the other units can react. And the only viable units in Lunatic+ are Mire-bombers, Vantage/Vengeance + Nosferatu sorcs and bow wielders (Sniper, Bow Knight, Assassin, etc.) - attempting to use other units in the harsh environment that is Lunatic+ will only end in frustration and soft resets. Because of the almost guaranteed presence of Counter on at least a few enemy units, classes that can attack from 1 or 1-2 ranges get rekt on the enemy phase - the enemy will just suicide onto you and have you die via Counter. Thus there becomes a stagnation in class variation - only classes who have enough self-heal to survive the enemy phase or units who cannot attack adjacent enemies have a chance of being used in Lunatic+. Falcon Knights (or any staff wielder, really - falco knights work the best) and Dancers may see use in gimmicky, <2 turn set ups - but even then, you'll still be relying on the reliability of Nosfertanks and bow-wielders. The game becomes an exploitation of win conditions/unsatisfying tactics/map rerolls. Of course, you could use the same tactics in Lunatic, but the design of Lunatic allows for flexibility in your choices - Lunatic+ basically forces you to adapt these tactics or be really, REALLY persistent in your approach.
After that first horrifyingly brutal playthrough (I allowed myself spotpass/DLC in my next one because I was just done with the game) I have gone back to Lunatic, and I don't regret it one bit. Of course, this is just my opinion and analysis of my experience with Lunatic+, you may think of it differently. What are your opinions on Lunatic+?
EDIT: Keep in mind that I have nowhere near the expertise of some other forumers and that my relatively small amount of playthroughs may affect my perceptions on the state of Lunatic+. Feel free to take my opinion with a grain of salt.
I'm almost through the main story for my 2nd Lunatic playthrough and am looking for a good father for Noire for postgame/DLC. Because I am undecided on whether I should make her a sniper/bow knight or a sorceror, I'd like input on who the best father is for either role. So far, the fathers that have been taken are: Donnel Gregor Vaike Stahl Frederick Henry (not married; planning to pair w/ Cherche)