Currently @ T400+, I'm currently on the way to finish my personnal challenge: domination victory as the Russians with this huge 12 civ pangea map immortal;
I usually play with fewer Civs, so I had never experienced full scale combat with modern units. Here is my list of shared experience from that game, feel free to correct/inform/reward
goodjob
me as necessary.
I made 0 effort to diplomacy, wiped out Venice by accident (only 2 cities..), then DOW left and right. My only friend was (oh surpise!) Shakka
. He eventually got wiped but I revived him latter on just because we were real brothers in arms! 
1. Honnor finisher is GODLIKE on huge map. 1 modern unit is 65 gold, this is the ONLY reason I was able to run on -200 deficit for more than 50 turns. You only need to destroy 4 units per turn, which is easy with AI's carpet of doom.
2. Gattling suck, period
. The range decrease is just too painfull. I had of course 5 or 6 range/logistic crossbows. But once arty/planes are comming online, you just lose them 1 by 1. Theirs strenghts is just too weak at this point. I never bothered building them past medieval.
3. Tanks are AWESOME! I was lucky since I needed no navy, so I could spare oil for that. Mobility is about everything late game, hit&run are so usefull. Really a good outlook oh how tanks really made modern warfare a completly different story
4. Cossacks are very very powerfull, basically come with a free 30% domage increase! No idea if that stacks with the +33% dmg to wounded units that you can get after.
5. Mixed feelings with autocraty. The -30% maintenance cost is really powerfull. All the smiles from the baracks/defence buildings were really needed since I cruised into happiness problems a lot. But after those basically 3 key policies, rest is a bit underwhelming. The % production boost and xp is quite nice, the %boost for 50 turns is good too (though I finished the timer, since war drags for long). Also I couldn't build Prora since I had 0 (out of 35+!) coastal city. I really wish I could have built the Kremlin in this game actually.
6. I saw Isabella use Air Swift a few times !
Speaking of airplanes, AI had quite a lot of them. Fighting vs 10+ planes is not uncommon late game so AAguns are just mandatory at some point.
7. I also made use of the usually most useless wonder: the Pentagon
.
I had more than 50 units to upgrade when I hit radar, so on purpose I delayed upgraded and waited for the Pentagon to pop up. Saved quite some cash here! Especially added to the Honnor policy, most late game upgrades were about 90 gold each.
To conclude, this game had been a blast. I've been fighting at most 5 AI's at the same time, with a constant -150gpt, with sometimes peak @ -23 unhappiness and yet crushed every oposition. Really felt like roleplaying the good ol' USSR with massive internal deficit yet dominating the whole world
But truth be told, the end is quite lonnnng, still have 2 capitol to take but have to cross about 30 more cities. Varsaw, here I come!
I usually play with fewer Civs, so I had never experienced full scale combat with modern units. Here is my list of shared experience from that game, feel free to correct/inform/reward


I made 0 effort to diplomacy, wiped out Venice by accident (only 2 cities..), then DOW left and right. My only friend was (oh surpise!) Shakka


1. Honnor finisher is GODLIKE on huge map. 1 modern unit is 65 gold, this is the ONLY reason I was able to run on -200 deficit for more than 50 turns. You only need to destroy 4 units per turn, which is easy with AI's carpet of doom.
2. Gattling suck, period

3. Tanks are AWESOME! I was lucky since I needed no navy, so I could spare oil for that. Mobility is about everything late game, hit&run are so usefull. Really a good outlook oh how tanks really made modern warfare a completly different story

4. Cossacks are very very powerfull, basically come with a free 30% domage increase! No idea if that stacks with the +33% dmg to wounded units that you can get after.
5. Mixed feelings with autocraty. The -30% maintenance cost is really powerfull. All the smiles from the baracks/defence buildings were really needed since I cruised into happiness problems a lot. But after those basically 3 key policies, rest is a bit underwhelming. The % production boost and xp is quite nice, the %boost for 50 turns is good too (though I finished the timer, since war drags for long). Also I couldn't build Prora since I had 0 (out of 35+!) coastal city. I really wish I could have built the Kremlin in this game actually.
6. I saw Isabella use Air Swift a few times !

Speaking of airplanes, AI had quite a lot of them. Fighting vs 10+ planes is not uncommon late game so AAguns are just mandatory at some point.
7. I also made use of the usually most useless wonder: the Pentagon

I had more than 50 units to upgrade when I hit radar, so on purpose I delayed upgraded and waited for the Pentagon to pop up. Saved quite some cash here! Especially added to the Honnor policy, most late game upgrades were about 90 gold each.
To conclude, this game had been a blast. I've been fighting at most 5 AI's at the same time, with a constant -150gpt, with sometimes peak @ -23 unhappiness and yet crushed every oposition. Really felt like roleplaying the good ol' USSR with massive internal deficit yet dominating the whole world

But truth be told, the end is quite lonnnng, still have 2 capitol to take but have to cross about 30 more cities. Varsaw, here I come!