Anno 2070 offers the perfect synergy of RTS, City Building and Trading. I recommend the complete edition because the Deep Sea expansion adds a layer of extra depth to the tech trees.

In Anno 2070, the size of your city is limited only by the size of your island--and there are some really BIG islands. If for some reason you aren't satisfied with your island, build some nukes, launch them, watch the pretty mushroom clouds and then move into your newly acquired glass parking lot (island). Don't feel like remediating nuclear radiation from your newly conquered paradise? Try sabotaging your enemies' main food source--destroy an oil tanker off the coast of an enemy island (preferably next to their fish hatcheries) and while he/she scrambles to clean up the oil, harass the cleanup crew with fast attack boats or helicopters and then send in your attack fleet. Even better, with the Deep Sea expansion, you can create tsunamis to wipe out your enemies' coastal holdings by destroying strategically placed geothermal power plants. After all, your citizens are worth more than your enemies' citizens, especially if your enemy happens to be the Eden faction... those hippie tree-hugging ♥♥♥♥♥! Pick the Tycoons and use the power of coal and nuclear energy to crush the little Eco ♥♥♥♥♥! There's no Captain Planet to help them against your rain of nuclear fire! Crush them and their tree covered islands and pave over everything with concrete!

Anno 2070 is not your typical city builder. As I explained earlier, this game is more of a hybrid City Builder, RTS and Trade Sim. Unlike traditional city builders, Anno 2070 has warfare. If warfare isn't your thing, you can play a peaceful game or you can eliminate your enemies through economic policy (hostile takeover). A hostile takeover is not as intricate as it sounds because all it involves is buying out enemy island shares until you have greater than 50% but, it adds another unique aspect to Anno 2070 game-play.

Another feature that sets Anno 2070 apart from other city builders is that you, the player, have 100% control over everything that is constructed. Compared to traditional city builders where the AI constructs buildings after the player zones an area for residential/commercial/industrial--Anno 2070 gives the player COMPLETE control over all structures: construction, destruction and placement. This is the perfect feature of the anal-retentive City-Building fanatic because it allows the control freak to CONTROL!

Placing buildings in Anno 2070 is almost like playing a puzzle game. Its always good to maximize space so when you're building in Anno 2070, be prepared to destroy and rebuild. I have over 200 hours in my current continuous game and I've rebuilt each of my major cities 3 times. I also razed and rebuilt the entire power grid across all 29 of my islands (largest map size). The reason for the rebuilding is pretty simple--I keep thinking of better and more efficient ways build, produce goods and house my citizens. My 3 largest cities started with max populations of: 29,000, 29,500 and 34,000 and each of them barely had enough power to keep on the lights. Now, those same islands boast populations of 34,500, 37,500 and 40,500 and each island has 1000+ excess power to share with the power grid.

Honestly, this game is a blast! The only reason Anno 2070 doesn't have 'Overwhelmingly Positive' reviews is because people hate on the Uplay DRM. I agree that its annoying but, its no reason to avoid one of the best city builder/rts hybrids of all-time.

EDIT: I noticed a number of people complaining that Uplay doesn't work for Anno 2070. Since I hadn't played in a few weeks I decided to boot it up and see if there was a problem. Uplay works just fine. The Steam version of Uplay is outdated. You need to update Uplay and everything works just fine.

The fix for this is so simple its mind boggling how many people fail to see it when its mentioned in numerous threads within the community hub. I know the Steam fan-boy knee-jerk reaction is to hate/blame any third party DRM so I guess I shouldn't be so surprised.

EDIT 10/17/2015: I see the reviews for this game keep slipping BUT not because the game-play is bad. The reviews are slipping because a bunch of ♥♥♥♥♥-ass Steam fan-boys hate Uplay DRM. Sorry boys but, Uplay works just fine and has done ZERO to inhibit my Anno 2070 gaming experience.

UPDATE 11/24/2016: Anno 2070 is still the best City Builder on Steam but, it doesn't matter because the Steam fanboys hate Uplay which, means, according to the fanboys, that Anno 2070 is a bad game.

UPDATE 11/23/2022: Anno 2070 is still here and the devs at Ubisoft patched it to use the new servers so the game will remain playable for the foreseeable future. I booted it up to check and all original functions of the game are intact. I lost my save files years ago so I'll be starting a fresh continuous game. I'm looking forward to breaking 600 hours of play.