Problem is: Panzer General had alot of units in the game... Civ 5 will not; although it's not known yet; 30 units seems to be a high number even for late game from estimations of the forum boards; which would give maybe 5 units for the whole first era.
So the whole 1 unit per tile doesn't even make sense... If you have 5 units for 1/4th of the game, it doesn't really matter if you can stack them or not at that point.
No Navy?!? (guess they said screw it, since they couldn't figure out how to make Carriers become more valuable than Battleships; this has to be the most pathetic thing I've heard so far... LAME! No Navy!)...
Very few roads.. 1 city defender... archers can shoot to across oceans

if you are landlocked with only 4 tiles available and surrounded by a massive powerful civ, your unit limit is 5 (4 hexes and your city). Of course, you'll be lucky if you have 5 units for a majority of the game.
Not sure what happened with the whole thing; Civ obviously can't be PG, and I think they figured that out too late, and now they are stuck with it (or we are stuck with it if we buy it).