A live action Scooby-Doo shouldn't work but 'Scooby-Doo 2: Monsters Unleashed' shows that it does

Story

The Mystery Inc. gang attend an exhibition at the Coolsville Museum showcasing all the costumes from the monsters they've caught and the mysteries they've solved. During the event, a masked man known as the 'Evil Masked Figure (I know) appears and steals some of the costumes and plans to create monsters. The Mystery Inc. gang have to stop him and prevent him from creating more monsters.
This movie runs like a very long episode of the cartoon and this works in its favour, it's not weighed down by any complexities and that allows it to double down on its own ridiculousness. If the plot was too complex the film would get boring and the last thing I want from the Scooby-Doo movie is to be bored.

Acting

While I watched the movie, I noticed that some of the actors were trying too hard to be like their cartoon counterparts which led to overacting. Matthew Lillard falls into this category, given the fact that  Shaggy and Scooby are the comedic relief of the group, they give the most eccentric performances which borders a very fine line between endearing and annoying.
The other actors don't have that issue as their characters are more muted. During many scenes, it looks like they are having fun. There are some characters moments that seemed a little out of place given how the characters act in the cartoon but I'll allow it because this movie is based on the cartoon.
 That being said there aren't any standout, award-winning performances, but that's not to be expected in this movie.

Writing/Direction

I found out recently that James Gunn who wrote and directed the 'Guardians of the Galaxy' movies for Marvel worked as a writer on this film. The writing and dialogue in this movie was very tongue-in-cheek and cringeworthy but I don't hold it against the writers too much seeing as this is a kids movie. It doesn't try to be witty and clever, it's humour is at the most basic level that doesn't always land.
This movie also has a lot of physical humour with characters doing things that make you laugh due to the sheer ridiculousness of the situation.
The movie was directed by Raja Gosnell, the same person who directed 'Big Momma's House', 'The Smurfs' and its sequel as well as the prequel to this movie. Now that I know this there is a common thread to his movies. They're mostly family movies with low brow humour and that's not always a bad thing.
From a technical standpoint, there's nothing to note, I didn't start this movie expecting to be amazed by the use of editing or the way the film was shot but I tend to look out for things like that when I watch movies.

CGI/Set Design

It has to be said that the CGI in this film is terrible, I'll forgive it though because this movie was made in 2004 for a budget of $25 million. Having a movie rely on this much CGI and not have the budget to cover it means it looks fake and cheap. Scooby and most of the monsters are completely CGI and it is very noticeable and it can take you out of the movie.
The set design reminds me of 'Batman and Robin', both movies have colourful characters and settings.
(I also have to mention that both movies have Alicia Silverstone in them)
In this movie, it makes more sense to have an eccentric look as it's a remake of one of the most iconic cartoons ever and said cartoon has a distinct animation style. Does the CGI and set design work? Not really. Do I give the people who made this movie points for trying? Yes, I do.

Overall Thoughts 

If I said this movie was perfect I would be lying, and if I said it's a dumpster fire that deserves to sit in the darkest corner of my memory. I would also be lying. For me, there is a huge element of nostalgia here because it's the first movie I remember seeing at the cinema. I saw this movie at 5 and instantly loved it, although I already a built-in love of Scooby-Doo.
This film has not aged well at all, more often than not I was laughing at the film rather than the jokes or physical comedy on screen. This movie is in the same vein as 'Batman and Robin' both films are so bad they're good.
The easiest way to watch this movie is to not think about it too much, turn your brain off and just enjoy. I guarantee that you will laugh at least once. This movie knows what it is and at no point does it ever try to be more than that. It sticks to its premise and has a consistent theme and tone throughout the entire film.
That being said there are moments that are laughably bad, but this is the movie that gave us this...

So we cant be too mad at it because Velma's makeover is iconic.