so, this bad mamba jamba is on sale on steam and I'm interested in delving into this genre. Question- how does it compare to Civ V?
There's a lot more to learn early on. Technology is much more passive and it is very difficult (and usually not worth it except early on) to stay ahead in tech. There are discrete provinces, but combat is largely uncontrollable once it starts and only tactical in the sense of positioning (e.g. luring an enemy across a river or into a mountain province to gain advantages).
Wars are more about building a web of alliances and finding ways to neutralize the enemy's advantages, such as taking control of a tactical strait with your navy or destroying the enemy army early on so it can't resupply.
Diplomacy is a lot deeper since in addition to the typical alliances, you have royal marriages (which can in fact impact gameplay in addition to relations - if you're diligent you can strategically royal marry when a monarch is about to die off without an heir, getting you into a position to force a personal union over the country), vassalization, protectorates, colonies, etc.
Factional differences are about gradually unlocked passive bonuses. Each nation (well, most any you'd play) has a unique idea set which unlocks different passives as you progress, and you will also choose specific ideas (e.g. colonization, religious conversion, offensive military, etc) based on your needs at the time or which direction you want to go.
EU4 isn't super comparable to Civ V because Civ is like a board game writ large with small bits of randomness (mostly map generation and AI). EU4 has more randomness and a lot more variables to deal with, so your job is figuring out which ones are relevant and acting on them. It can be really rewarding when you seize the moment and manage to get a large advantage over a long-term rival, but you can also get stuck in bad situations - sometimes through no fault of your own - for a long time as well.
Oh, also an EU4 game (1444-1821) lasts around 30 or 40 hours. Maybe more. It does depend a lot on how much you like to expand.
tl/dr; Higher learning curve, more rewarding, more addictive, slower paced. I think I have played Civ V a bit more simply because it's been out longer, but EU4 will occasionally steal half a weekend from me. Fitz's recommendation to watch a bit of gameplay is a good one, since it will give you a much better idea of the play-by-play.