I am playing a game in which I lost to Gahndi in the space race (by alot), but continued playing to get a feel for the modern era. The main issue I noted is global warming; it's slow and steady, which will eventually halt the game (too bad).
Anyway this is what I noted.
1) Battleships/destroyers are great for reducing city defense (20% per shot)
2) Bombers less so (stealth only 8%). Fighters don't cause collateral damage and have more of a chance to be intercepted (more so than stealth).
3) Artillary are more or less obsolete *if* the city is near the shore. Otherwise, you'll have to pound a 80% defense city 10 times with stealth. (vs 4 times w/ artillary). Bombers are great for reducing units, but will stop at 50% damage (which I don't think is the case w/ artillary collatoral damage). Also they can get intercepted readily.
4) Critical. Invading stacks must have air support; ie a carrier with jet fighters, or SAM infantry.
5) Enemies with air superiority will destroy your civ by pillaging it to death, ie that one aluminum resource, every turn. Air intercept missions can help, their range is the base range of the fighter (8 squares?). That's the only defense against long distance pillaging.
6) The reverse is true; if you enjoy air superiority, you can pillage your opponent to death. However, if the opponent has lots of jet fighters, there is little you can do except have huge stacks of stealth bombers.