[Spoilers] Not bad, entertaining. But doesn't compare with Chow's best.

Or his second best.

Let's begin with the comedy. Perhaps I've watched too many Stephen Chow movies (perhaps not perhaps, more like most definitely) but the jokes used here aren't as laugh inducing as his past works (e.g. Kung Fu Hustle, Journey to the West 2013 even) and didn't come flying into your face as fast. It seems most of the best ones were saved for the trailer (e.g. the incompetent police sketching scene). The opening scene (the third rate "zoo"), perhaps the most important part in terms of attracting and keeping the audiences' attention, is pretty weak.

COMEDY

If you were to ask me which were my favourite gags in, for example, Shaolin Soccer, then I would reply "basically the whole movie". But in the Mermaid, they were few to the point that I'll go ahead and list the ones I found, at very least, mouth-curving:

1) The cross-dressing mermai...-man, with the forest of pubic hair to match.
2) The gold-diggers, upon learning the value of the watch, swiftly diving into the pool to retrieve it. Personally, I would take this joke to the extreme. For example, the male protagonist (hereafter called Rich Guy), as a filthy rich businessman, might own a pool or tank full of piranhas, and this will be where the female antagonist (hereafter known as Bad Gal) throws her million dollar watch. And his harem will jump in, regardless of the danger.
3) The bouncers/security tackling (and suplexing) the female protagonist (hereafter known as Mermaid).
4) The gory explosion of the goldfish was both amusing and disturbing (trademark Chow violence).
5) The subsequent selfie with the goldfish corpse.
6) Octopus man getting shot with a poison dart and reacting to it nonchalantly. And then proceeds to criticise the shooter minutes later.
7) One of the mermaids who curiously, has a monobrow.
8) The two men abusing Octopus man's tentacles, and Octopus man trying his best to convince them to leave it alone. (I can't help but feel this gag was used in a past Chow movie though). And reused in the same movie (Tentacle cooking scene). Not as funny the second time. But the ink spray escape was a nice touch.
9) The Rich Guy assassination scene. (but this joke was already used and done better in Kung Fu Hustle so not as funny to me).
10) Rich Guy constantly throwing bundles of money at people who annoy him.
11) Good old toilet humour with Rich Guy and Mermaid getting dizzy and vomiting (classic Chow).
12) Of course, the incompetent mermaid sketching scene.

The last one happens to be last joke full stop. In the last half hour ("third act" I believe film connoisseurs call it?) it basically takes a major dramatic turn and the drought of jokes happens. This is not out of place for a Chow movie but what does seem unusual is that in his other movies, the humour continues, even if lives are at stake. For example, the psychological thriller third act of King of Comedy and the final series of fights in From Beijing With Love.

So comedy-wise, it is nowhere near Stephen Chow's Magmum Opus, Kung Fu Hustle. Not even near Journey to the West: Conquering the Demons. I'd say it's about on par with CJ7 which I didn't like much but at least it had the excuse of being intended for children.

MORAL TO THE STORY

Like many of (maybe all?) Chow's movies, beneath the equal amounts of genuinely clever humour and toilet-level yet still funny slapstick, there's always a message to impart to the audience, a moral to the story. The main message is obviously the relentless pursuit of profit and money leading degradation of the environment and the animals that live in it. It felt pretty ham-fisted to me (including the what I assume to be actual footage in the opening minutes) and the message sold better elsewhere (as far as effectiveness of environmental awareness goes, Princess Mononoke tops the list for me). I'm sure there are other values (love conquers all etc) to take out of the movie but I'm not good at analysing those sort of things.

CHARACTERS & PLOT

While the two main characters of Journey to the West: Conquering the Demons held up the humour side of the movie pretty well in Chow's absence, in Mermaid, I only felt a longing for Chow to play an acting role again. Mermaid (the character) was okay, good even. Rich Guy mainly just shouts and act angry/annoyed. I'd say Octopus Man had the best comedy acting range, most exemplified by the first tentacle abusing scene. Those are Stephen Chow trademark facial mannerisms right there. I'm sure the whole thing was Chow's idea (do this! act like this! make this face! say this! and say it in this way! etc).

When I finished watching the movie, I felt that some things were unexplained or not explained too much. What is with Bad Gal and her "tsundere"? Does she or does she not care about money? Is she or is she not romantically interested in Rich Guy? Does any of this have anything to do with her zealous attempts to kill Mermaid?

Slightly more backstory for the Mermaid tribe, the Rich Guy (to give his cookie-cutter barebones vanilla "rags to riches" history more substance), and especially Bad Gal would be nice.

I'm sure we can improve/flesh out the plot a bit from the 1 and 1/2 hours runtime (pretty short by modern blockbuster standards). Of course, if there is no increase in jokes accordingly (something in short supply) then there's not much point.

I acknowledge that maybe it's the way in which I approach this movie that affected how much I enjoyed it. Is it a comedy movie with dramatic elements? Or a drama with comedic elements?

Having said all that, for non-Chow fans, it's still worth a watch. You could do a lot worse. For Chow fans, watch it still, for his sake, if not yours. Because it's Stephen-f'ing-Chow.

OTHER/RANDOM

Is it me or does Mermaid look strikingly similar to Shu Qi, the main actress of Journey to the West (2013)?

Some interesting cameos and not so cameos (that I noticed):

Tsui Hark.
Iron Stomach (?) guy from Shaolin Soccer etc.
Chow's fat friend from Kung Fu Hustle and fat Shaolin brother from Shaolin Soccer.
Badass (and effeminate) Arm Ring martial artist from Kung Fu Hustle.
Octopus Guy is Sword Guy from Journey to the West (2013).
Bad Gal is Mute Girl from Kung Fu Hustle (she was the last person I recognised, I mean compare the characters).

Is the cross-dressing mermaid the same cross dresser in past Chow movies?
Is the incompetent sketch artist the fish demon from Journey to the West (2013)?

What's with the Japanese speaking woman, who also happens to be the only actual Japanese actor in the movie? She had two main functions (one early in the movie, on near the end): demonstrating the fish killing device (and taking glee from it) and directly giving the orders for the massacre to go ahead. Since this was a mainly mainland China-funded film, my best guess would be, it had to meet its "hate on Japan" quotas. Obviously the intent was to parallel the Japanese woman's actions/behaviour to real life: whaling/dolphin-killing and more importantly (since China doesn't really care about that since they're responsible for some of the fish stock damage, then again most countries are also to blame but I digress) reminding people of imperial Japan's WWII actions (which China definitely does care about). Smells like selling out to me. At least the hamfistedness of the environmental awareness serves a (positive) purpose.

It seems most or all of the cast spoke Mandarin (with some token English) but I watched it in Cantonese. In Cantonese, most people spoke Cantonese (with some token English) and a few minor characters spoke Mandarin. In both voice tracks, the Japanese woman spoke Japanese.

Rich Guy throws the Mermaid into the sea, who is badly cut, shot at, and pierced with a harpoon and dragged for who knows how long, not to mention general concussions body impact, and expects her to have the strength to swim away?

Kung Fu Hustle (maybe even Shaolin Soccer) had better special effects. I know that graphics aren't Hong Kong/China's forte, but for a blockbuster I would've expected better. I mean, Kung Fu Hustle. A decade plus old movie looked more impressive. Even today, it still looks impressive.