I wrote the following on Boardgamegeek and it seemed worth preserving locally:
There are four basic types of 18xx:
- Run Good Companies
- Where’s the Free Money?
- Put Things Together (typically mergers or company pairs or synergies)
- Timing Games
Clearly some, most, all(?) 18xx games are mixtures of the four camps in various degrees and at various times during a given game. The private sales to companies in many games is a free-money element, but so are destination runs with multi-jump stock increases and the extra 40%-50% in free capital given when floating companies in full-capitalisation games. The mergers in 1817, 1824, 18EU, 18C2C etc are clear plug-things-together moments etc, but so are the synergies between privates and majors in 1846, 18C2C etc. The portfolio management of the 1825s, 1853 and the like fall out cleanly as timing games, but 1826’s focus on getting the right trains into the right companies arguably does too.
Few if any interesting 18xx seem to be purely any one of the above meta-types, rather they move and shift focus across a balance of those points over the course of the game.
Amusingly, 18xx players can also be classified across the above four criteria, and like the games, the Run Good Company players are considered the least interesting and the Free Money players get all the despairing head shakes.
Other structural divides centre around elements like:
Fast trains: Some games tend to focus on train rushes, and coming out on top after the dust has settled. The key metric is how large a fraction of the purchase cost is the typical run value and how many times they’ll run. 1843’s trains generally need to run three times in order to cover their purchase cost, but will often only run once or twice before rusting. Another key metric in this space is whether trains sometimes rust before they ever run. This usually means that the key decisions in the game are made leading up to the early cheap permanent trains. 1830, 1841, 1843, 1849, 18Mex etc all tend to feature blistering train rushes (though 1843 skips the cheap permanents bit). David G. D. Hecht designs (as a broad for-instance) tend to have rather sedate/processional train progressions.
Low or high income: A basic measure of how rich the game is, especially as a function of train purchase and company floatation prices, but it can also be as a function of more basic operational costs (eg tack-laying costs). 1830 is the most notorious example of a low income game, but 1849 gets in there too. 1843 tries to be a low income game and often is. 18C2C and most of the Double-O Games designs are high income games.
Tile manifest: Are the tile limits a significant function of Good Play? 1830, 1843, 1849, many of the Wolfram Janich and some Double-O Games designs fall into this camp. In other games, the tile manifest is explicitly generous, or at least rarely if ever a consideration in Good Play (1817, 18C2C, most-but-not-all David G. D. Hecht designs, etc).
Stock appreciation vs dividends: Which is more important: dividends and cash in-hand or stock appreciation? 1830 is the grand-daddy of stock-centric games with 70+% of player scores descending from stock appreciation. Most Mark Derrick designs are heavily cash/dividend focused.
Certificate limits: Are key strategies in the game focused on managing certificate limits (yellow fever, forbidden forest, variations in share density, number of presidencies, etc). Most any game with a classically coloured stock market falls into this camp with 1830 and 1870 being the two most notorious examples. 1817 plays in this space with share densities and thus the balance between stock appreciation and dividends.
Liabilities: Are investments possibly significant liabilities? The classic form of this is the potential requirement to buy a train out of pocket. Not all 18xx have that property (eg the 1825s, 1860 etc), and several of the Double-O Games titles feature not-very-onerous loans which smooth the edge there. The 1825s, 1853 and to some extent 1860 conversely impose no requirement for companies to own trains, just financial hiccoughs if they don’t.
Balance of share values: Which is more important, owning the best shares or owning more shares? Does that change over the course of the game? 1846 for example is notable in being readily won while still not at paper limit – it is a game in which owning better shares is commonly more important than owning more shares. Conversely 1830 is the poster child of owning more shares typically defaulting to being better than owning fewer better shares.
It is worth nothing that the shape of the stock market does not feature anywhere in this list. 2D and 1D stock markets are effectively identical, just with rather more complex price movement rules for the 2D markets.