Elements looks at the parts that are included in the set. If it includes parts that are new, in new colours, or rare, then it gets a higher rating. This also includes the minifigures.
Swooshability is pretty simple. Do kids and adults like swooshing it around making silly sounds? Is it conducive to play? Things like moving parts and cool functions will help this.
Build takes a look at the quality of the build. Is it strong or weak? Does it use good build techniques, or is it a pretty standard one on top of the other?
Design / Appearance looks at the aesthetics – does it look cool? Is it a pretty good representation of it’s real life counterpart (if it has one)? Does it make people say “Whoa, that’s LEGO?” or “Hey, that’s cool!”
Value for Money takes a look at the listings on Brickpicker.com (a great site for LEGO investing, and figuring out the values of sets over time) and Bricklink.com (for current sales) including price per element, it’s estimated value growth or loss in the future, as well as my own thoughts on the elements included for the price
Collectibility looks at whether it’s worth getting for the collection, in relation to other sets of it’s kind by LEGO, and also in relation to elements included.
Finally, there’s the overall rating. This will be a total of all the scores listed above. The first four areas are scored out of 20, with the last two out of 10 for a total out of 100.