Looking at games with respect to mechanics, sociality and theme reveals that there are many games that we could argue are comparable in their joyful realisation of mechanics and sociality but differ greatly in theme - or more specifically the amount of theme present (how abstract is the game). Othello and backgammon are highly abstracted while King of Tokyo and Snakes and Ladders have a stronger theme, they craft a scenario or a world. What are the merits or otherwise of these approaches...
Theme can play a few roles in a game, it doesn't just have to be putting pretty pictures on all the components. Themes can help players understand the game and its mechanics, if there is a logical link between the theme and the rules then players will learn and remember the rules more easily. It is easier to conceptualise climbing ladders and sliding down snakes than going up blue ribbons and cascading down red ribbons.
This gets more important as the complexity of a game increases. Our brains like to tie memories to narratives and real objects and so creating a large sweeping game full of alternative mechanics all working like a well oiled machine is just hard when the theme is abstracted away. However if you embellish those ideas with a strong theme for a game like Warrior Knights then we can not only play the game but really enjoy it.
Theme can also provide something of an initial spark of interest. Ticket to Ride is a lovely game where there is a certain level of abstraction and you could quite easily convert the game to a fully abstract version which still had colour matching and set collecting and denial and all the fun player interaction. Giving the game this amount of theme however (at least for me) provides an initial jump-on point for wanting to find out more.
Even a very thinly themed game can allow for a different set of achievements that transcend the win-lose mechanics of more abstracted games. If you are playing Agricola and you come last in points, you may still be happy that your semi-abstracted farm has some nice pens with happy sheep in them. Similarly, if you win a game of Pandemic, then you have saved the human race (a pretty nice sense of achievement)
Even games that aren't dripping in theme as much as these are easier to talk about with friends afterwards. Recounting a moment in the game where your fireball card slew my Ice Queen card just before I was going to win the game could have been broken down into abstract set collecting and card values and so forth, but is certainly easier to chat about.
What I am realising though is that theme is something of a double-edged sword. Themes are specific, the mechanics of a particular game may be a precise match for your little gaming group but the theme may be off-putting. People might not want to be a giant city-destroying robot, or a little-pony-unicorn, or a zombie or a race-car driver or even a galaxy spanning race of purple aliens. Here is one of the real risks with theming a game - it can alienate people in the same way as it can appeal to them.
Maybe Chess has hit some sort of sweetspot here, it is quite abstract in some ways, but you are still moving and 'attacking' with your knight, your powerful queen and all those pawns in an effort to protect your weak king. Apply a different theme to chess and you get a variant that appeals to different players. A Simpsons themed chess set has identical mechanics, but is doubtless more appealing to some and less to others...
Clearly the approachability, portability and adaptability of a deck of cards is very high and that has great appeal to many people who wouldn't consider themselves gamers at all. There is also that appeal of honing attention onto a nice mechanic in abstract games.
So where does this leave us, probably in a place where the more options a gamer or a gaming group has the better. People can hopefully find their own sweetspot in terms of the games they enjoy best. If there is a nice range of abstract through to heavily themed games then people can taste and consume things from all across that continuum.
Perhaps we also shouldn't be uptight about reskinning games. I get the impression that if FF reskinned the Star Wars X-Wing game using zany dwarven submarines vs aquatic monsters that they would get flack for reskinning. But Dwarven Subs vs Kraken Hordes could be a super game and may appeal to those that weren't drawn in by the Star Wars theming.