I've only played Ireland so far with 3-players. To spice it up, sub Japan Bullet Train action for Irish Locomotive...
After a few games, I'm happy sticking with a fully defeatured locomotive for 3-players. I've also grown to hate the De-urbanization action - too ornery and nasty. I do want to try Ireland with 4-players though.
Barbados - as a 1-player map, replayability may be low, but cube randomness makes it unique every time. Action selection restrictions make for some interesting strategic planning.
St. Lucia - an excellent 2-player map. A very different game with goods starting on every plains and river hex, no goods growth, and a large number of 'stubs' abandoned after moving the goods from those hexes.
Agricola:ACBaS is a stripped down version of Agricola for two. Streamlined, simplified, no luck, and no food or feeding, just optimizing of farmland and animals. With such a quick playtime, this a pretty good filler. I could see it getting pretty stale but my wife enjoys it.
Dominant Species is an epic area control and worker placement game. It's very tactical as you don't know what elements and cards will be coming next turn which I suspect may be its downfall.
The game is quite long and bad for players with AP. The randomness of the card and chit draws and lack of ability to forward-plan is a major drawback. However, the game is engaging and there is high player interaction.
Glen More is a resource management, tile-laying eurogame with a neat little market mechanism and a novel turn-order mechanism. The game scales well between player counts with the ghost player die an interesting mechanism to balance the lower player counts.
The quick playtime is the redeeming factor here; there's a lot going on but not that many interesting decisions.
Hamburgum uses the rondel action-selection mechanism but suffers from low-player interaction. Working the ships (impacting players' ability to sell for maximum market demand) is a very interesting aspect and I wish it had more impact on the game.
Innovation is a clever card game where the cards played in front of you represent technological advances that give you advantages in some respects. You can invoke the power of a technology (dogma) and the player with the most of the representative symbol takes advantage of said power benefiting himself or directly impacting other players.
You really need to know all the cards well and which pair well together. I find it difficult to plan a long term strategy and often the more tactical player, not stuck on any one path will be successful. I'm always building a big infrastructure with grandiose plans while others are scoring and pushing the game to end quickly. Also, the higher player count, the more chaotic the game is. Quite good for 2-players though.
It's clear to me that there are many false choices in the game; there appear to be many options when, in fact, there are few. Get your science up and focus on military. It's that simple. It's fun to explore the different paths, but after a few hundred plays, it comes down to 'get your military up and plan for war with the leader.' As a result, luck of the draw is worse than it initially may appear.
It scales well though the 2-player (2 - 2.5 hrs) is very different than 4-player (4+ hrs).