The criteria I use to evaluate a d20 adventure includes the following:
1. Interesting and varied encounters: I look for unique encounters, allowing for a variety of role and roll playing.
2. Motivations for NPCs and Monsters: or some detail of how they interact with their environment or neighbors.
3. Logical: the adventure should obey a sense of logic that clever players can use to their advantage.
4. Writing Quality: this includes foreshadowing, mystery, and descriptions that bring locations and NPCs to life.
5. Ease of DMing: Clear maps, friendly stat blocks, skill check numbers, player handouts and illustrations.
I don't give much weight to text density and cost per page... I'd rather pay a lot for a small clever mystery than pay a little for a huge repetitive monster bash.
I don't give much weight to new monsters, prestige classes, and magic items... they can add a little variety to an adventure, but to me they are minor decoration.
THE BASICS: (not exactly spoilers)
The adventure is 96 pages long, cover price of $15.95 American.
6 pages of credits/legal/advertising
5 pages of adventure overview and plot development
7 pages of NPC motivation/description
5 pages of city adventure
9 pages of wilderness adventure
48 pages of site-based adventure, some of which is in wilderness setting
The adventure is designed for 4-6 characters of levels 7-9. The adventure contains a huge number of encounters, and depending on how thoroughly your party explores or how mission oriented they are, some encounters will be bypassed. In my estimation, they breakdown as follows:
Approximately 30 combat encounters
Approximately 20 non-combat, negotiable, or avoidable combat encounters.
Approximately 30 environment encounters (traps, trick doors, things to examine)
The encounters range from very easy to the incredibly difficult, with most at the midpoint. It appears that the difficulty levels closely match what is outlined in the Dungeon Master's Guide for suggested encounter variety.
The adventure is fairly setting neutral and could be easily dropped into any world, though it may require a some DM adjusting for some of the NPC motivations to jive if your game has a detailed political structure. The basic plot is a missing person investigation which leads to a site exploration, with clues pointing to a second site exploration.
There are references to monsters, items, and spells in the d20 books by Sword and Sorcery studios "Relics and Rituals", "Creature Collection", and "Creature Collection 2". For the most part, the adventure is playable without these books (more on this later).
The adventure takes place at two distinct sites, and seemed almost to have been designed as a two-part serial adventure. The two parts, while linked by theme and an evolving overall plot, do stand alone individually and could easily be used this way.
The adventure does not contain boxed text. The adventure is a series of site-based adventures (rather than event or timeline driven)
THE SPECIFICS: (Some Spoilers Follow)
1. Interesting and varied encounters: (4/5) The adventure contains a very wide variety of encounters in a variety of terrain types. There are opportunities for every class to shine, although a rogue would be almost a necessity, and the final 1/4 of the adventure has less available for druids. The combat and non combat encounters are intermingled, and even the combat encounters will often start with a little banter as the intelligent opponents attempt to get a feel for the party before attacking. There is almost no repetition in the encounters, which is very surprising for an adventure of this size. Your party will never sigh as they begin yet another encounter with the same monsters they dispatched in the previous encounter. There are a few encounters which seem like dangerous traps, yet turn out to be nothing-- (one cleverly hidden doorknob will cause your players to sweat before trying to turn the knob), but the false danger schtick gets done more than once and for me it loses its appeal. There are also a few more traps than I would generally prefer, which tends to slow down a party as they become over-cautious. I rate the adventure 4/5 for interesting encounters, there is a minor bit of repetition with some constructs and trapped doors.
2. Motivations for monsters and NPCs: (5/5) This is a place where the adventure truly shines. Careful detail has been given to almost every monster, providing motivation and explaining how the monsters interact with each other and the party. This attention to detail is an incredible help when I need to improvise as the players pursue an unexpected course of action. Even the wandering monsters are provided with detailed lairs and a definite purpose for being "out wandering" and contacting the party. The civilized encounters, while short, are well done and provide good opportunities for role playing. If your group especially likes city encounters, there may be some DM work necessary to work the local politics into your world or to provide some non-adventure related encounters such as at a shop or tavern. I rate the adventure 5/5 for highly detailed motivations of monsters and NPCs, as well as role playing suggestions for the DM.
3. Logical: (4/5) Everything in the adventure seems to follow logically based on the set-up. A place where nobody has been for many years would necessarily only have undead or constructs to be encountered... places that are open to the outside world tend to have animals and beasts. There are enough clues that clever players will be able to anticipate a few encounters, and they will feel good for having figured it out (or they will slap their foreheads and say "I should have known!") The adventure does contain a few high-magic elements, such as an artificially illuminated underground cavern populated by exotic fauna brought in by one-way teleporters. The adventure also contains a hollowed out mountain... again something that might be hard for players to swallow in a low-magic world.
4. Writing Quality: (5/5) The quality of the writing is excellent. Creatures and locations come to life with evocative descriptions. Most encountered creatures are described as beings rather than simply stat blocks. Even without boxed text, the DM will have no problems describing locations, smells, and sounds to the players. The first half of the adventure is an explicit mystery, (where is the Rainbow Mage?) and an additional plot twist as the players discover that there is more to the Mage than they anticipated. The second half of the adventure is more of a straight find-the-MacGuffin as the players must explore an evil temple.
5. Ease of DMing: (4/5) The maps are located at the back of the book rather than at the beginning of each chapter. Some wandering monster stat blocks are located in the appendix which will require a small amount of page turning. There are good internal illustrations for the DM (which could be shown to the players), but there is not an illustration booklet and there are no player handouts. There are a few monster and magic spell references to non-core rulebooks, which may cause a bit of a pause to DMs who do not own them. There are enough stats provided that a DM can get by without the supplemental books (and people who own the books will enjoy getting to use them), but I would have preferred to see some advice on alternate spells or perhaps longer descriptions of monsters for people who don't own the Creature Collections or Relics and Rituals. The stat blocks are clear and concise, the keyed maps are aesthetic and easy to read, the errata corrects what few editing errors I could find. There is an obvious loose string at the end of the adventure which the DM may have to write themselves, depending on how doggedly the PCs wish to pursue a villain.
FINAL WORD:
Overall I am extremely pleased with the adventure and rate it a VERY high 4/5. This is the first adventure I've reviewed, and don't want to "use up" my 5s in case I should ever happen to find the holy grail of adventures. The 2nd half of the adventure, in which the players explore an evil temple is similar to Demon Gods Fane which was released at about the same time. I have not yet playtested the adventure, but I would estimate it would take about 10 sessions of 4-5 hours in length, based on the speed that we play.
Supplemental material is available.
Errata is also available online.
EDIT:
Since this review first appeared, I've read many more adventures with a very critical eye. Only one has approached Rainbow Mage in quality, and I feel that it is only fair to adjust my rating to reflect my appreciation for how good this adventure is. I've upgraded my rating to 5/5.