So, we just got off Oasis of the Seas, and quite honestly, were very underwhelmed, especially with the food. MDR had good service, but below average to terrible food. My wife's Prime Rib was inedible (you could not cut through it). We were also surprised at how small the buffet (Windjammer) area was for the size of the ship, we only had 2,900 on our sailing and the Windjammer didn't have open seats at breakfast. Food there, especially desserts, wasn't the best. Not sure how they manage with more than that on the ship. Maybe it was because the Solarium Buffet area wasn't open but from 11-1 each day. Entertainment was hit or miss, though I will say that the Aqua80 show is amazing and made up for how bad "Cats" was... (I had read all the posts on cruise critic of people making fun of it, but I thought, "well, I enjoyed it on land... it can't be too bad..." Yes, it can...). The ice show was OK too.
Surprisingly, I actually found myself bored on Oasis, which was about the last thing in the world I ever expected. Maybe this was due to COVID... Other than the casino, or karaoke on the promenade, or going on the sea deck, there wasn't a lot for a 50ish year old to do (i'm not into rock walls, ice skating, or the flowrider thing). I enjoyed the waterslides, though they have these things on Carnival and DCL as well. To sum up, they had a lot of "bells and whistles", but IMHO, were very lacking on the activity schedule (again - could be due to COVID). That being said, I can totally see where those in the 12-18 year old age range would love the ship.
Also, I HATED the fact that it seemed like in order to get any decent food, you had to pay an upcharge. No poolside eateries (other than "Loco Fresh"' which I will admit was very similar to Blue Iguana on Carnival and was included), so if you want a burger, you have to go to Windjammer (or pay extra for Johnny Rockets). Also, ice cream service only went until 5:30pm. If you wanted any after that, you had to pay extra at the "Sugar Beach". I also hated that the sports bar area charged for food for things like chicken wings, chicken tenders, and fries. We never ate at any of the upcharge places. Lastly, the Promenade Cafe was a joke as the food was terrible there (again, whoever is in charge of desserts/pastries on RCCL should be fired). The International Cafe on Princess is light years better than this...
We did enjoy Coco Cay, especially the fact that it had a pool. Food on Coco Cay was actually better than it was on the ship. We didn't pay for the waterpark area, so can't review that. All in all a nice addition to the cruise. Is it better than Castaway? I'd say that depends on what you are looking for. Personally, we probably enjoy Castaway a bit more, but there is absolutely nothing wrong with Coco Cay. I actually might give the nod to Virgin's Bimini Beach Club, which, although much smaller than the other two and not being it's own "island", was great for what it was and the food was amazing...
This was our 3rd cruise back post-COVID and probably our least favorite so far, though we did have fun and would not hesitate to do another Oasis class ship, it's just that we can usually find a similar Princess itinerary for less and if we are going to splurge a bit, we will probably do Virgin Voyages. We have also cruised on Disney Magic and on Virgin Voyages Scarlet Lady in the past few months. TBH, Virgin blows most everyone else out of the water where food is concerned and I would say entertainment, though "different" is up there with DCL and RCCL. We were really impressed by the food quality and inclusions on Virgin. If you haven't tried it, do it. For instance, the ice cream there, which is open until 10pm is gelato style and included! The DCL cruise was a pretty good cruise as well. Food (especially desserts) were really, really good -- much better than RCCL. Also, the entertainment, as always, is really good, though I'd say that you really need to be a Disney fan to enjoy it. I also enjoy the full size movie theaters on the DCL ships and the included on demand movies on Virgin, DCL, and Princess. (As mentioned above, on RCCL, they were $11.99 a pop...)
Our next cruise is on Mardi Gras in a couple of months, so we will get to compare it to Oasis, which is what I think Carnival is targeting with this. We've only done one other Carnival cruise (Sunshine back in 2015 - surprisingly great cruise, with a good deal of thanks to the amazing Jamie Dee for making that cruise so fun...), and had a great time, so we are looking forward to that and being able to compare.
I'll also say that overall, we really enjoy Princess as we find that the food is mostly pretty good (especially Alfredo's and the Buffets on the Royal Class ships) and you never feel like you have to shell out extra to enjoy it. Maybe it's our age group (late 40's / early 50's), but even though there are no rock walls or waterslides on the Princess ships, they always seem to have multiple things going on all the time (my favorite being the time we stumbled into the "Dirty Irish Songs" sing-a-long) and we enjoy the vibe on the ships, though we also enjoyed that Sunshine cruise, so hopefully our Mardi Gras cruise will be similar!