KGB: How is it that you are blessing your Sea units when they can't travel on land?
On most maps I played there is a temple on the coast that they can reach.
KGB: The only real way to carry a hero is to pick one up on a port or in a coastal city which is kind of hard.
Not harder than having him/her embark/disembark and lose 1 turn or more. And you can do it also in swamps, there's plenty of swamps communicating with water. They're sea creatures after all, not flying ones. And you can bring the hero on water with a flying creature and from there go on with the serpent.
magian: Aren't galleons stronger than 25 strength anyway? And they cost 20 gold? Why would I shell out 550g for a serpent?
If I'm not mistaken, currently Galleons allow max STR 45. I didn't use them enough to talk, but maybe 45 STR for a galleon is too much and cost 20 is too cheap. I think a ship strength progression 15->20->25 would be better, or maybe 15->25->35 max. Maybe serpents could have +15 in sea/swamp instead of +10, but I think the price is fair, the same with Kraken. They give some more options compared to other units. On some maps (like Lonely Isle) they pose already a big threat. Just personal opinions, though.
magian: Giants are just walking around with 25 strength. Blessed giants in the hills are 40 strength. Plus giants have legs and can therefore walk ON LAND!!!
In this sense maybe you're right, I think serpents should have an edge on water, compared to other 2-turns units, if they had +15 in water/swamp they would be 30 STR against most other 2-turns units with 25. But then again, if you can bless them, they would get 35 STR on water that would be rather frightening.