Is this a hit board game? The number of BGG ratings and rank (13648) don't reflect that. Does it stand out in some way from the multitude of similar games?

Here is my take. There 3 types of options:

Web based services that fully implement and enforce rules for their games

• Boardgamearena - the best selection in this category by far. These days games are added much faster than normal players will be able to keep up with so there is always plenty to explore. Very large player base, for popular games you will find matches quickly. Good match-making and lots of play modes: real-time, turn-based (with customizable time allowances), Arena, Tournaments. Generally high quality implementations that tend to stay visually true to the physical version of the game. Many games have good tutorials. The premium subscription is not strictly required but an excellent value if you use the site a lot. BGA has been invaluable in my boardgame journey. It has allowed me to learn and try hundreds of games and I must have bought at least 50 physical games based primarily on my BGA experience. Too many favorites to list.

• Yucata.de - moves slower but over the years it has built up a decent repertoire and it has some real gems that you won't find elsewhere. Primarily for turn-based play (unless you find a group of people who commits to quick turns). The UI is a bit quirky but after getting used to it I like a lot of things about it. In my opinion Yucata has the best undo and replay/review implementation out there. My favorites here are Grand Austria Hotel, Newton, Mottainai, Taverns of Tiefenthal, Lorenzo Il Magnifico. Rajas of the Ganges (and Rajas Dice), Targi, Fields of Arle. Yucata has "sold" me a bunch of games too.

• triqqy.com, happymeeple.com, brettspielwelt.de, rally-the-troops.com, boiteajeux.net, warchestonline.com are some other sites that I visit for specific games. These have smaller player bases but worth checking out to see if they have one of your favorites.

Virtual tabletops that don't enforce the rules

• Tabletop Simulator is a desktop app that's available for purchase on Steam. As the name suggests this is a physics based 3d tabletop that allows you to play a huge number of games thanks to a passionate community that implements and provides these via the Steam workshop. You will find just about everything here. The main downside (to some) is that game rules are not implemented or enforced. It's primarily a 3d simulation of the phyisical components. Many games implement some level of assistance using the built-in Lua support, for example they might automate setup or have a button for end-of-round cleanup. But generally it's up to the players to follow and enforce the rules of the game. I don't play a lot on TTS but I use it all the time to get a feel for a game or its components.
• Tabletopia is a web-based alternative to TTS with the same caveats. Smaller selection of games and less flexible UI, smaller (and less involved) community. Some games can be played for free, others require a subscription.
• virtualtabletop.io - is an open-source reimplementation of playingcards.io. You can think of it as a 2d version of TTS. I like this approach a lot, especially for card games or abstract stuff where the physics simulation and fancy graphics wouldn't add much. Relatively small but passionate community.
• Vassal engine - a Java based open-source desktop app. Lots of modules and a passionate community. Worth checking out especially if you are into wargaming.

Apps that fully implement the rules

There are a lot of apps out there, some for mobile, some for desktop (many available on Steam). Most require a purchase. The quality of implementations vary greatly. Some support online multiplayer, some don't or there is no playerbase. Some have nice snappy implementations, others have very poor UIs or go the other extreme and create an overly fancy UI that is too removed from the physical game. This is generally my least favorite option, I will almost always prefer a good BGA or Yucata implementation over an app. There are a few exceptions: Ascension, One Deck Dungeon, Onirim, Sagrada and Paperback are some where I like the app version a lot.

Mine:

• A couple of very cheap sectioned trays. Shallow enough to make grabbing tokens easy and enough sections to organize them. We use these for pretty much every game with tokens.
• A side-table to help deal with table hogs.
• A couple of those foldable dice trays. I don't actually use them for dice but as a flexible funnel when bagging things.
• Notepad, pencils, eraser
• An empty tea tin. I use this for some games where you frequently draw items from a bag because it's a lot faster.

I am guessing that it may be referring to this. Note that the post is on the Stonemaier site so it's their side of the story. Some searching also turned up a later analysis in a BGG thread.

In a hindsight given the extremely wide distribution, HUGE number of copies sold and many followup products all of this doesn't seem very relevant.

To be fair I was expecting a lot worse from a videogame website. It may not be the absolute top 10 but it's a plausible list of some of the most complex games that the average boardgame player is likely to encounter.

For comparison, BGG search for gameplay weight over 4 and at least 100 votes
(which needs to be taken with a grain of salt too but it's what we've got)

Example summary for Tiletum:

setup

• board:
  • populate action wheel with action tiles (optional) and bonus tiles
  • 3 bonus tiles for king track (no tile for last round)
  • bonus tiles for map spots based on player count
  • town and fair tiles on track, fair order marker on the picked towns
  • cathedral tiles and random build reqs. Remove unavail cathedral
  • contract and character markets
  • 10 dice in bag (2p)
• players:
  • markers on score track, turn order track, king track (p1 on bottom!)
  • place houses and pillars on their spots. There should be 2 of each left for each player as their available supply
  • 1 of each resource
  • 1 gold for p1, 3 gold for p2

play

• prep: draw, roll and place 8 dice (2p)
• action:
  • p1 flips and applies corruption token
  • dice values +/- for 2 gold. affects action and # resources
  • pick die, get bonus tile and resources, perform action
• king: points, bonus tile, player order. bottom wins tie. from negative snap to 0 after
• fair: merchant or house in town to qualify
• cleanup: refill wheel tiles, rotate wheel

Tasks (free actions) at any time:

• gain a resource for 2 gold
• fulfill contract
• place crest (food cost). Apply bonuses
• build cathedral (only 1 of each type!)
• use helper tiles from storehouse

Important:

• many house spots are only for higher player counts. With 2p there is at most 1 spot in each city
• some house spots have bonuses
• players can only get 1 cathedral piece per type!

(should add a section about scoring too)

For pure teach Nithrania - Game in a Nutshell and JestaThaRogue are my favorites. For playthrough based teaches JonGetsGames is good.

Before You Play is kind of a hybrid, they often do a teach followed by a playthrough. BGG's gamenight (have to search for "gamenight") often has good teaches and playthroughs, especially when it's Dave Arnott's turn to teach. I also enjoy Slickerdrips' playthroughs, the teach in these is a bit more loose but still helpful.

When you are in a hurry 3 Minute Board Games or The Rules Girl can be helpful but these are not as thorough.

Thanks OP for the excellent post, the BGG link markup is very helpful!

Sensible production and packaging choices would be a good start.

It's fun to think about which modern games could have existed in the middle ages or antiquity.

Component complexity is probably the biggest limiting factor. Some components would have been very difficult or impossible to produce. The available printing technologies is a major one. Depending on how far we go back easily shuffleable cards are probably out and cards with lots of text or complex symbology are almost certainly out. So are fancy boards. Simpler boards (chess or go grids, hex) are fine. Meeples, dice, coins, tokens, bags, cups are easy.

Rules complexity might be another factor since it would be more difficult to record and reproduce very complex rules. Some kind of thematic connection woudn't hurt either. I guess you could try to explain Star Realms as heavenly chariots :)

Abstracts are a category that works well since we have a bunch of examples of those actually existing. Simple dice games, bidding games, certain drafting games should work as well.

Some specific examples of games I like to imagine existing in the past are War Chest, Onitama and Azul. Thematically they would fit well, simple rules, manageable components.

I wonder which of the more complex euros could have worked. Perhaps a simpler version of Castles of Burgundy? Fewer building types to keep component and rules complexity under control. Or maybe something like Ra.

Apparently I am "Expert" but I don't feel like one. I just like playing lots of games. I have too many games but very few unplayed. The "as many as you can" is bound by money, space and time to play.

Ascension is my most played by far. It's one of the earliest deckbuilders and the first one (I think) with the river-style market which has been used in many other deckbuilders since. The developers have done a great job exploring various mechanisms in the expansions over the years and most of the content is available in the digital version too. My favorite sets are the ones that use Insight (the amber gems): Dreamscape, Delirium, Deliverance.

Besides the game mechanics the great art, music and the smooth app make it very chill and enjoyable for me.