I've been play BE for about 7 hours, and have played CIV5 for about 150 hours and SMAC for probably the same. I'm playing on normal difficult, standard speed, medium graphics.
vs CIV5:
Negatives:
-Units are very difficult to identify between - their logos look very similar, and are all the same colour. The 3D models dont 'pop' against the game world, in terms of contrast, like they did in CIV5.
-Taking down cities is incredibly difficult. Including casualties, you will need a force of 10-15 units for a mid-game capital, even if it only has one defender. City bombardment does a huge amount of damage, far more than any mid-game troops. (Best tactic to kill a siege worm is to lure it into range of a city).
-The characters are completely lifeless and boring. The leaderheads aren't animated (on medium) and diplomacy is essentially copied from CIV5. The elimination of luxury resources, and the smaller number of resources in general, makes diplomacy irrelevant except for bribing the AI into attacking eachother.
Positives:
-Aliens are very interesting. A better mechanic than barbarians, and present a fun challenge. (Taking down your first siege worm requires the commitment of 50% of your nation)
-The turn end times seem quicker.
-Quests are reasonably interesting.
-Units seem cheaper to build.
-Tech web design is more interesting, though more easily exploitable if you can get a free tech, and select from the outer rim.
-Covert ops is now better streamlined than in CIV5 BNW
vs SMAC:
Negatives:
-Leaders and setting is less interesting. Diplomacy was better in SMAC than CIV5 anyway, and BE diplomacy is worse than in CIV5.
-Apart from modern 3D graphics the game terrain and unit design is less remarkable.
-No animated wonder videos.
-You can only build 2-4 cities without running into health problems mid game. As a result big, sprawling empires are impossible. Even puppets cause health problems.
-Wars are much less interesting. With so few cities, and 1UPT, every war is about luring existing enemy units into range of your cities and ranged units, taking them out, then piling with overwhelming force onto the enemy cities and slowly grinding them down.
-Unit upgrades system is much less exciting than unit design
Positives:
-Hexes
-Modern UI
The game has been fun to play, though I feel this is more the initial thrill than anything else. I'm not sure if I will replay after first game.
I wish CIV would move forward and copy some aspects from games like Endless Legend (a visually more impressive, and more interesting, if flawed strategy game). Overall I think the AI simply cannot handle 1UPT, and the amazing sneak attacks and near-losses I experienced in CIV3/4 and SMAC I have never witnessed in CIV5 or BE.
This game has the potential to be fun after a 'Gold edition' with all patches, DLC and expansions included. Until then, 6/10.