Most 18xx fans will tell you that categorically, 2-player 18xx games aren’t “real 18xx experiences”.
!%#@$% those guys (within the bounds of law, of course). I haven’t played it yet, but I’ve watched a video of 18CZ’s 2-player mode that introduces a bot player that is jointly-controlled by the players. Heavy Cardboard did a play through with the bot, Vaclav, and it seemed to be a very good experience (they both said they really felt it was a full 18xx experience).
1889 is often touted as a “2 player friendly” version of 18xx because it’s a tight map with interesting (read: challenging) terrain. I never remember, but 18AL may have glaring defects? (Maybe I’m actually thinking of 18GA… Alabama… Georgia… who can keep those states straight in their heads?).
1846 also has a well-regarded 2-player mode (if you can find a copy; here in the US they can usually be found used for $40-$50, sometimes less).
I do think most 2-player experiences in 18xx will be fundamentally different in texture to 3+ player games, which is also how I feel about 2-player euro experiences vs higher player counts (head-to-head as opposed to free-for-all; more players = more noise = more interesting problems without, necessarily, your opponent having to directly interfere).
1889 is very much a “1830-alike”, in that it has almost the exact same rules as 1830 but set on a different map with a few additional changes. 18Chesapeake, recently hitting streets, is also a 1830-alike. I think 18AL is also 1830-alike.
1846 has quite a few differences and is often considered more "euro"y than 1830-alikes.
18CZ is by Lonny Orgler and Lonny’s games all tend to be similar in feel; a lot of things are streamlined. The major commentary about Lonny’s games are that they are “operational” style games and not “stock market shenanigans” games; you tend to win Orgler games on the map during operating rounds whereas 1830-alikes are typically won in the stock market rounds.
- 18CZ is available for purchase directly from Lonny’s website, https://lonny.at and is reasonably priced (for an 18xx) game.
- 1846 is between printruns but if you can find a copy, it’s often used as an introductory game (even though it is very different from a 1830-alike)
- 18Chesapeake is a 1830-alike that was kickstarted and just landed; it is not, however, listed as 2-player-able but I think the designer has posted on BGG that you can give it a try and proposed the starting cash and share-limit if you want to
- Other Lonny Orgler games often come with 2-player modes: 1824: Austrian and Hungary Railways recently landed after its kickstarter and it includes a 2-player map.
- DON’T BUY Poseidon - I did and I think it’ll be a fine game… but I don’t think it’s the gateway 18xx experience that it was once played up to be
- DON’T BUY 18Lilliput - Or do… but know that it’s a very, very distilled 18xx experience and probably not enough of an 18xx experience to get a feel for what 18xx actually is
1861/1867 is a Kickstarted two-games-one-box 18xx that’ll be landing soon and in retail immediately following fulfillment that boasts a 2-player mode as well as a (likely pointless) introductory game mode.
- Don’t wait for 18DO! There’s 18xx goodness already available!