Modular vs Integrated expansions

Having recently done an expansion for Crusaders, and having done 3 expansions for Eminent Domain and one for Isle of Trains as well, I have noticed a particular style I like to use when creating expansions, and I've identified two distinct types of expansions: Modular and Integrated.

Modularity

A modular expansion is one with several distinct modules that can be added in various combinations. These can be good because they allow the players to use the modules they enjoy, and simply ignore the ones they don't care for. It allows players to customize their experience. Undoubtedly, this is something that some players will appreciate.

However, it also requires playing each module at least once to determine if it works well for your group, and it requires some effort to curate the expansion content to provide that perfect customized experience. For a group that loves a game and plays it all the time, one that's willing to put in the effort and plays to find the perfect combination of modules, this could be fine. But in today's market, I wonder if players will put in that time and effort? Or would they prefer to just buy a curated expansion, where the "best combination of modules" is the only thing provided?

Another down side to a modular expansion is that because of that modularity, the pieces of the expansion may feel bolted together and disparate rather than feeling like a seamless experience.

Integration

An integrated expansion is one where the new parts play off of each other and off of the original content. When done well, this type of content fits seamlessly with the base game, and it can be difficult to differentiate the new stuff from the old.

This loses the opportunity for customization provided by a modular expansion, but it gains the curated feel, and doesn't require any work on the part of the player to get to the "best" configuration.

Another down side to integrating an expansion is that it may be more difficult to remove the content when you want to play the game with new players. For an insular group who plays the same game many times, an integrated expansion may be preferable, while for a group where new players come and go with each play, it may be more difficult to pop the expansion content in and out.

My personal preference

It's probably clear in the above paragraphs that modular expansions aren't my preferred format. Well integrated, expansion content fits together with the base game in such a way that it feels like it was always there, or like it belongs. I find something attractive in the thought that the expansion integrates so well that a new player might not be able to identify the new content from the old.

Looking at the expansions I've done, I think it's clear I've attempted to go for integration over modularity:

In the Eminent Domain expansions, you simply add the new tech cards, shuffle the new planets into the deck, and the Fleet, Mining, and Political Influence tiles tie it all together.

When I first played Isle of Trains: All Aboard (which hasn't been published... yet) with the publisher, they were skeptical going into it that the game really needed an expansion. After we played, they said they were surprised how well integrated the expansion was, and that it was not obvious the expansion content wasn't just part of the base game in the first place.

Crusaders: Divine Influence is about to ship from China, so not many have played it yet, but my goal with that one was to seamlessly integrate the new content with the old. I replaced the Influence action with something more involved, and I added new buildings and a few factions. If you know the rules of the base game already, then playing with the new content should be easy to pick up. Learning the game for the first time with the expansion content included will be a bit more complicated than learning just the base game, but I have had some success teaching the game that way most of the times I have played the expansion with strangers.

Conclusion

There might be a temptation to make expansions modular, because as a designer it can be easy to think that's what players want, and it abdicates the responsibility of curating the expansion to the players. My advice for designers is to consider the game you are expanding, and that game's audience. In this day and age, with thousands of new titles coming out every year, is modularity really the best format for your expansion? Or would your audience be better served with a well integrated, curated expansion? For most of the games I work on, I think it's the latter.