Well, In my curent game, I am trying a one-city challenge (standard pangea map) as India, Prince difficulty... (focused on farms, not money, so my city has reached some 27 citizens, making over 100 research and culture per turn, I think it is the only way to try to keep up technologically)
You could not increase your empire even if you wanted to (one city forever)... you can only (instantly) destroy cities if you conquer them.. they just vanish...
It can go fairly well untill the Rifleman/cavalry tech (I am seriously struggling to keep up techs with the English, which is a new perspective for me in CivV), and then it starts to get tough... as empires rise, they will inevitably get a tech lead over you, as well as superior troop numbers...)
it is cool, game runs fast, it is hard...
At the very start I was at war with persia (to my east, with a huge lake between us)...
they sent several units which I managed to destroy with a swordsman, elephant archer and a catapult... (war lasted for some 50-60 turns more, but never a single unit from Persia going my way (they were busy probably busy with England, even managed to take one city from them)
Then, the Ottomans came... but unlike my Balkan forefathers, I pushed them back, AND destroyed Istanbul (which surprisingly was very close to Delhi, and their nearest city)... I got lucky with the Ottomans because they were being hammered by the English, but I still lost 2 out of my 5 units (one badly damaged longswordsman and two catapults remaining)... Quick peace with Ottomans (they settled 3 cities in the area of Istanbul probably within 15 turns
Then, I look at the map, England eats Mongolia and Ottomans, I recruit new units and go into offensive from the south...I destroy 2 cities england took from Ottomans (while loosing 3 units, they constantly have cannons for garison and longbowman nearby, a killer combination)... (while this goes on, I constantly build troops so I have at least 4 units at each time)... England does not try to invade me, instad focuses on Mongolia and Ottomans (who btw keep loosing)... I take one big English city near me, again with losses, and I retreat... England settles a city at the very spot and it grows quickly... in the meantime, I defeat several settler - riflemen duets England sends to colonise near me... Another offensive - again, city destroyed... keep pushing - York.. If I take it, London is in striking distance... Terrain unfavorable, all hills...cannon can not reach York, only artillery, lost 3 rifleman while destroying the city... London in sights, but badly damaged, and England piles cannons, knights, rifleman nearby (my only remaining units - a rifleman at 3 or 4 health, a cannon at 2 health, and an artillery...) Retreat as fast as I can... While recuperating, england builds a new city at the place of York... And it is harder and harder for me to follow tech-wise... Mongolia is eaten... Ottomans reduced to new cities (build after I destroyed Istanbul), as they lost most of the old ones to England...
I am guessing I am next in line to get a whooping by that sadistic queen, but I will do my best to defend my city... 3 artillery and 2 rifleman awaiting for the wave of enemy troops...
So, to sum things up... one-city challenge is awesome and I will certainly try it again (at the moment I am trying to get my first cultural victory)...
Resource limitations are CRAZY... playing a whole game without horses is not that fun, but it is challenging... I have no coal... I have no oil... its going to get tougher by every single turn, and I am loving it