Androrc the Orc
Emperor
The problem with the "Ironclads" technology in Civ3 was mostly, IIRC, that it was a dead-end technology, not that it was a single-unit technology.
I like some of those, but I think "Medicine" is a bad name for an industrial-era technology. Medicine existed much earlier than that. I think in fact that choice of name "Penicillin" for the tech in Civ5 was rather good.
I'd like a longer classical age, right now it's really short and sometimes only lasts one turn (complete the Great Library when you get Philosophy -> Civil Service). They should fill the Cataphract gap and add a new technology between Horseback Riding and Chivalry that adds late antiquiy heavy cavalry. One reason for this would be the addition of Byzantion. They should have Cataphratcs as a UU, but they're neither suited to replace Horsemen (too early) or Knights (too late).
To keep Horsemen useful, they could get a bonus against ranged units, and the research cost for Horseback Riding should be lowered.
Sanitation?
I don't think alchemy can pass itself off as a technology. But hey, neither can monotheism, and that's been in almost every civ game.
There are a few broken tech paths that should be fixed. First, you shouldn't be able to get to infantry without first getting rifleman. Second, the time between muskets and rifles is also very short.
How many players go down the bottom path; the nuclear path? If you are going down the diplomacy or science victory paths, you don't even need to go down the nuclear path.
I hope there aren't too many techs towards the end of tree. Don't get there very often (either won, dominating so hard that I can't be bothered to finish, or lost) and most of the time the strategical choices aren't that interesting.