Fun: rated on how fun the Easter egg was to run for me and the overall map in general.
Zombies in Spaceland - very replayable map, amazing wonder weapons, neil, and great boss fight m1 with wind core/xquisite is so fun to use)
Attack of the Radioactive Thing - easy to get setup, great map design imo, and really fun Easter egg to run
Beast from Beyond - fun map to get setup on, quick Easter egg and although tanky, the boss fight is pretty fun - although failing meph constantly might get you hating the map, but I found it fun to see how fast I can get to meph
Shaolin Shuffle - tedious but kind of fun quest, but the katana and chis put this map above rave for me
Rave - the crossbows and map design and rave mode are great, but the boat ride is dreadful, im personally not a fan of the map layout, and the steps and boss fight are boring, but still a great overall zombies map through all the cods I've played.
Easter Egg Difficulty: tbh all of IW's EE steps are easy through all maps, but this is if I had to rate them.
Shaolin Shuffle - tedious, long and boring steps, and it's really easy to get destroyed while doing steps because of ninjas or zombies. Steps like the dragon symbol just suck, the hangman requires a cheat sheet, and the disco step is not easy as well, plus without the right setup the 3 rat king phases is an ammo dump.
Attack of the Thing - also tedious, cheat sheet is a requirement, and so many locations and say you misclick or get the math wrong or look at the wrong number you're at 1hp in the chemistry step and if a zombie hits you you're done, all in all just alot of leg work.
Beast - the escort neil step can sometimes lead to a down if the door doesn't open, but not that hard overall.
Spaceland - without the right setup the seticom defense might be tricky and could get you killed.
Rave - I guess killing the slasher in time after the picture can be tough
Boss Fight Difficulty: man does IW have the hardest bosses in all of zombies, never have I ever gotten my ass kicked by bosses in any other zombies game.
Meph - what can I say but just brutal. You need to be dialed to beat him.
Spaceland Alien - im putting this above beast cause he can really beat your ass if his slow hits you or if he TP's on you, and it's so easy to get cornered. Plus the extra alien per person is the most brutal scaling I've seen.
Beast - brutal mag dump but patience is the name of the game. Once you play patient and treat it like a bullfight it really isn't too bad. Plus the arena has enough space for the blue flames to not be too big of a problem, but it can get hectic and messy with multiple people.
Attack - Bomb step is brutal especially with a team, plus that acid step final phase can get cramped, and the death ray weak spot bit can be tough if frog decides to slam in the middle. Mana Up laser cheese helps but the lasers aren't that hard on its own once you know the route.
Shaolin Rat King - the only hard part is the acid one (heart I think?) and the ninjas and dpsing the guy but the boss fight arena is chill and mana up for the acid step makes it easy and negates the only hard part about the fight.
Rave Slasher - if you're dying here you're buns, super easy fight.
I realized my fun rating is basically what overall would be, but ig I haven't done just the map by itself and how fun it is as a map without the Easter egg involved so here -
Spaceland
Rave
Attack
Shaolin
Beast
WWs and map design play a big factor here, plus the overall feel of the map. Space land and Rave have plenty of soul poured into it, and they're so unique and incomparable really. Attack I'm a big fan of, love the 50s vibe and the color scheme of it, just wish the MAD wasn't locked behind the box and there was some buildable instead. Shaolin is cool of the chis and the Katana is awesome, but the map design to me isn't anything special, and beast is just a pain. The venom X is a chore to get, the map design is cool but it also isn't, but the layout is kinda weird, and a bit confusing especially to navigate through and find the box.
I'd really put it highly amongst other CODs, and if anything I think it's the best zombies experience that has come out as someone who likes Easter eggs and is not much of a high rounder. BO3 (the golden boy of zombies) have great iconic maps and good EEs but it's too easy IMO, whereas BO4 has great EEs and maps but not all maps are strong (Alpha Omega, Tag) I haven't run BO7 yet, but wow, directors cut is an amazing addition, the super Easter egg and celebrity character unlocks are so unique and awesome, and all the boss fights are excellently crafted IMO and super rewarding. Even Beast's boss fight although hard and tanky, makes sense and is so unique from a design standpoint. BO3, BO4, CW, and even BO6 bosses really pale in comparison (BO7 does look promising though)