I believe the combat log is accessable by pressing CTRL-TAB.
I have to agree that the lack of information is often frustrating. I'm not talking about obscure details here, but important things, like how do you get to play the infernals? A new big feature in the latest version is you can switch your civilization to infernals mid-game. From what I've read in the wiki:
The founding of the Ashen Veil brings the Infernals into the world and significantly increases the Armageddon Counter. Human players who found the Ashen Veil have the choice of leaving their initial civilisation to the AI and taking over the Infernals.
How excited was I to try this out, rushed to be the first to research the Ashen Veil religion, and then ... nothing happened.
Looking thru the civilopedia, under Hyborem's entry, it said "Your civilization cannot build this unit". I was playing the Sheaim, you know, the dudes who like to summon stuff. I picked them because, of all the evil civs, I thought they'd be most likely to want Hyborem to be summoned. Nowhere does it mention they Sheaim can't do it.
So yes, maybe this major game mechanic could be documented somewhere, and include all the relevant details like who can/can't summon the Infernals.