First, the overworld. This may just be the best overworld in ZC. It's big, it's varied, it's interconnected, and it's full of secrets and sidequests. Honestly, even if the quest lacked any dungeons at all, I think it would still be an amazing quest based off the overworld alone. You've outdone yourself Twilight Knight. It's truly spectacular.
The world itself. Unlike most quests, I actually felt somewhat invested in the world. It feels like a real world you're exploring, not just a collection of maps. The NPC dialogue is also incredibly funny most of the time.
There's also the attention to detail. Just little things like the sunglasses or hat that you can wear add a lot of detail to the world. Or things like talking to the trees after completing the nature sidequest, or the "gypsies" (which was a brilliant twist tucked away in an obscure line of NPC dialogue).
Of course, there's also the graphical style. I don't how much I can say here. It's good. It's really good. I love what you did with the Pokemon mountains combined with old-school DoR. It's got a unique graphical style that's fantastic.
The dungeons... the dungeons I'm mixed on. Some of them, namely 2, 3 (especially 3), 5, and 6 were great. There was certainly a bit of style clash going in terms of design philosophy (i.e. it was really clear I'd walked from a TK quest into a CastChaos quest), but they were CastChaos at his best. I feel they incorporated everything I like about CC's design philosophy (the creativity, the surrealism) while eschewing all the bad (confusing triggers, cluttered rooms, etc). 7 and 8 weren't bad, but they had some minor annoyances. 1 and 4... Not a fan of anything in 1, really, and 4 did some annoying side warp shenanigans I'm not too fond of. The final dungeon was cool, but relied far too heavily on backtracking. In general, the dungeons were what I want to see from CC, but there were a few missteps along the way.
Custom bosses were kind of hit or miss. While 2.10 bosses have basically fallen from favor, some of them were pretty nice in a nostalgic sort of way. The boss of level 3 especially comes to mind. Her sweeping the room with lasers was really fun. But a lot of the later bosses seem to quickly devolve into hordes of enemies or bosses that stood in one place doing nothing. It was kind of disappointing whenever that happened because I know CC can do better than that. With the final boss, for example. He has a phase where he just summons enemies, which was boring. And then suddenly there's bullet hell patterns and giant energy blasts and escape sequences and it's awesome. It seemed weird that even within the same boss fight, there could be such exciting and such dull moments.
Now the story... I know I praised the worldbuilding and the NPC dialogue, but the plot left a bit to be desired. The Rebonites were interesting, as were the three artifacts (setting aside that the name "Orb of Fierce" is kind of hard to take seriously sometimes), but... well...
While we're on the subject of the story, there's an elephant in the room I feel like we have to address. We all know English isn't CC's native language, and his writing can be awkward at times. In his solo quests, I look past that because I know he's doing the best he can do. But in a collab project like this, it was incredibly noticeable every time a CC string showed up. I feel like I could point out every single string he wrote. I have no objections with CC writing part of the plot, but I don't understand why TK didn't edit his strings from grammar afterwards. It seems like a simple thing that would've done wonders for immersion.
So where does that leave us? A quest with a well-constructed world, the best overworld I've seen in ZC, dungeons that range from "not perfect, but pretty good" to "well it's not awful but it's not really good either", an average (albeit unique) story, decent 2.10 bosses, lots of interesting secrets, and a one-of-a-kind graphical style. I feel like, overall, it should come out to a 4/5. But the weird thing is that, for me, it feels like the quest is more than the sum of its parts. It's got its fair share of mistakes, don't get me wrong. But those mistakes never really stopped me from enjoying it. Even at it's worst, when I had to skim the help thread to find some obscure secret in a dungeon, it never felt like any more than a stumbling block to keep me from reaching the next awesome bit of world exploration again. So I'm giving it a 5/5. That doesn't mean the quest is perfect by any means, but it appeals to me in all the right ways. Great job, both of you.
In conclusion, Urdolf.