I haven't been through them all, so I'll just comment on the ones I've played, and as the civs I've played.
1. WWII (America, Japan) - Lot of fun if you like industrial era warfare. Japan's start can be overpowering in the hands of a human, but I like the way planning your unit moves just right gives you a good chance at several cities on the first turn, including Singapore. Nip infantry are a fun unit, but my favorite unit in the epic game is the marine, and doubly so in this scenario. With a few workers running around, Tokyo turns into a very productive city, as do a few on mainland Asia. If Japan has time to get these cities to max potential, they're nigh on unstoppable. I was mildly underwhelmed by America. It was still fun trying to stem the tide and buy some time for the mainland to produce, but the downtime once the Japanese fleet turtled at Saigon was a bit of a drag. Between amphibious attacks and hide and seek naval warfare, this one gets a 7/10.
2. Fall of Rome (Anglo-Saxons) - The Franks are a nice buffer state between you and Western Rome. I love the barbarism tech path and the scenario-specific units, but my favorite aspect is how they managed to create a map that really puts you in the scene and gives you the feel of a bloated, dying, though still formidable in direct confrontation, Rome that doesn't realize it yet. The fortresses and roads away from cities are a major part of that. I agree with the post above that the Huns should have a better mounted unit (maybe a three-move horseman), but that didn't affect my game much, since I basically used them as a diversion for my enemies until the game was pretty much won and I had a substantial force in Ukraine, having just wiped out the Ostrogoths, keeping one barracks city only, and decided the risk was almost nil, at which point I wiped them out. A very interesting aspect of this scenario is the free unit support. Because of it, I surprised myself by actually building defensive units for each city to free up my barb units for mayhem. Eight-city elimination fits this scenario like a glove. All in all, 8/10.
3. Napoleanic Europe (Britain, France) - Excellent scenario. If the AI knew how to handle amphibious invasions, it would be even better, but c'est la vie. The overall imbalance of the civs, unit for unit, is a nice aspect, and the diplomacy required worls well. Together, they build a wonderful pallette of strategic options and considerations. Set up a murderers row of cannon/grand batteries and frigates as France, and you can make sure Britain is unable to use the Channel very much. I did notice after the first fleet or two got hit with this, the AI began cutting its ship movements one tile short to stay out of artillery range. Normally, war weariness is my least favorite part of the game, but in this scenario, it somehow seems to fit, and even add to the fun. Maybe it was the motivation WW gave me to eradicate the British as the French and vice versa. While it would probably help to increase road movement to 4, as said above, my only real complaint is the AI razing cities. I understand why the option's available, and see where it could be useful, but it still irritates me in a no-settler game to see it happen. Still, I give this one an 8/10.
4. Age of Discovery (England, Spain) - Fun the first time because of the new concepts and units, though I was disappointed to find out the Sea Dog can't be used anonymously. With that being the case, England should have the option of building normal privateers. Fun the second time because of conquistadores in their element. It's amazing how quickly you can overrun the native civs with them. With Spain I deliberately abstained from continental conquest, so maybe I'll play it a third time and hit Portugal early to take Dias' Voyage. On the negative side, there's just too much potential treasure, and once you've seen the map one time, you should never be beaten to the hot spots. Hell, you can just settle the Caribbean, Central America and the South American coast and win easily. 6/10.
5. Rise of Rome (Rome) - All the others are nice, and have their own quirks to love, but this is the one I keep going back to. I'm currently playing it for the third time as Rome. Padua makes for a nice citizen pump to colonize the Balkans and Eastern Europe, and Pisae can serve the same function for Gaul and the Iberian Peninsula, but the real beauty of this one is the legions. I rarely use fortresses in the epic game, but I love parking about 4 legions outside, say, Carthago Novo, having three of them throw one up, and using that as a base of attack. They really help you control the road chokepoints. The tech tree is good, even if the Philosophy beeline seems to be a no-brainer. I saw the thread on Macedon/Persia, and have to mention that in my first game and the current one, Macedon fought them to a stalemate (should continue in this one, since they built Hadrian's Wall), and in the second game, Macedon had actually taken Asia Minor when I threw my lot in with them, cutting off the Macedonian attack and finishing Persia off myself. For anyone about to play this one for the first time, Temple of Artemis is pretty powerful here, since it doesn't expire. This is definitely my favorite conquest, 9/10.
EDIT: Meant to mention the rest of this, but forgot.
I've started the Middle Ages a couple of times, but for some reason just can't seem to get into it. Also started Sengoku once, didn't read up on regicide, and tried to take out a barb hut with my king. Oops

. I've got a feeling if I could ever get over the hump with those two, I would enjoy them, but just can't seem to get there. Also tinkered with Mesopotamia for a few turns. Meh, building's not my thing. The ones I've finished though, except for AoD to an extent, have all kinds of replayability for me.