Yes I would agree that moving beyond - Hello World - can at first seem daunting inside a Modular enviroment. And sadly there is not as much documentation on this aspect as there is on the more general elements on the system.
But I also feel that to a certain extent the reason for this - is that once you move beyond single action modules to site wide - portal implementations - that there are almost as many ways to move forward as there are sites to develop.
Given your comments above - it is entierly feasible however that you could build the whole review engine in a single module. With the actual layout controlled at runtime thru querystrings - and maybe some form of skinning if you want variable layouts for each category.
default.aspx?tabid=50&cat=1 - select a category
default.aspx?tabid=50&cat=1&review=23 - select a review
With the "enter a review" also handled inside the module:
default.aspx?tabid=50&cat=1&new=true - create a new review
The module uses the querystring info to turn on the appropriate Panels of Info for display at runtime. In this way the majority of your module is self contained.
Admin tasks such as Editing / Moderating / Deleting reviews can also be handled inside the module - by simply turning on ADMIN related buttons if the users has the right permissions - this could also include INLINE editing as well if you so desire.
Westa