As a big fan of Scooby Doo since forever, of the pro-Sander Schwartz Scooby Doo films- the ones since Chill Out Scooby Doo!- Moon Monster Madness was for me one of the weakest(although none of them are at all bad, even the weakest Music of the Vampire, two of the best Scooby Doo films- Big Top and Mask of the Blue Falcon- came from this period actually). That said, it's still worth watching, and Scooby Doo fans should find much to like.
The animation is great, with bold use of colour, colourful and atmospheric backgrounds and while not the smoothest animated Scooby Doo film out there it's nicely drawn with a nice mix of classic and modern Scooby Doo. The music fits very well and has a really groovy vibe while also using music and scoring appropriate to the mood, may it be light-hearted or suspenseful. On the most part, the writing in the Scooby Doo films is most enjoyable and Moon Monster Madness is not an exception. The dialogue is goofy without being too silly and good-natured, with some nice homages(like Ellen Ripley from the Alien films) with some very funny and sweet moments with Shaggy and Scooby. The story is not without its faults, but it's diverting still and has a solution that's not too obvious or over-complicated as a result of being too predictable or trying to do too much(Stage Fright was a good example of the latter).
On the most part it's fun and with some nice suspense, Shaggy and Scooby's friendship is one of the franchise's joys and it's as ever charmingly done here, the film also uses its unique(for Scooby Doo) space setting very imaginatively. Shaggy and Scooby are funny and endearing, Fred's likable and there are some fun supporting characters, Sly and Ridley being good examples. Not to mention the alien, it's very coolly designed and has a genuine creepiness without being too scary, to the extent where you'd start to think that it was a real monster. Great also is the voice acting, the gang are beautifully voiced(Matthew Lillard being the standout, though Frank Welker shows remarkable consistency considering he's the only one who was there right from where Scooby Doo began) and Malcolm McDowell and Jennifer Hale are particularly good in the supporting roles, Mark Hamill's a nice addition too.
Moon Monster Madness does have some erratic pacing though(but not all the time), with some scenes chaotic and others dull. The scene after the reveal for my tastes went on for a little too long and felt like padding, but the biggest issue for me was the friction/jealousy between Daphne and Velma, it didn't feel necessary and a little clumsily handled, Velma also came over as annoyingly bratty rather than resourceful, like a few of the Scooby Doo films made around the Mystery Incorporated period and after. In conclusion, good fun but not one of my favourite Scooby Doo films(Witch's Ghost, Zombie Island, Big Top, Goblin King). 7/10 Bethany Cox