Opening caveat: I play dominions almost exclusively as multiplayer. This will obviously colour my post.
There's
this tool to peruse the assets available to a nation (out of game of course!). Pretty handy if you don't want to start a game just to see what each nation can and can't get. In addition, before any "real" game it's fairly customary to run short test games (I do 10-20 turns) to see what works and what doesn't (what if any kind of bless? scales? what scales? research priorities etc.).
So while the interface is crummy as hell, people don't actually play things going in blind.
PvP is mostly about adapting your strategies on the fly. Each nation has certain strengths and weakness and pretenders can focus or diversify those. This is most evident in the midgame, once people have some decent research in a couple of different schools of magic. In a multiplayer game here I'm playing a nation with a ton of skeletons. People have started countering them with specific anti-undead spells. I can switch back to using recruitable soldiers, I can start using spells that improve the mobility of my skeletons. I can try to spread my undead wider than my opponents can their anti-undead mages. I can use remote attack spells to kill off enemy mages from several provinces away. I can recruit assassin's to try and do the same (admittedly non-magical assassin's aren't in vogue right now).
There's plenty that I can do, despite having a very focused nation (strong air magic, undead reanimation). And this whole back and forth countering and counter-countering is what keeps me (most of us?) playing the game.
Now it is true that you generally need mages and research to adapt (those anti-undead spells require specific paths and a specific research to become available), so adapting on a turn-by-turn basis might not always happen (army scripting & recruiting aside). But Over the course of a few turns things definitely shake up. Talking about that same multiplayer match; I was recently fighting 1v1 against an opponent. I was gearing my research, recruitment and manoeuvring to counter everything he was throwing at me. Very recently I was attacked on another front, by another nation requiring me to adjust what I was doing to counter the new threats that became apparent.
Some things to note about Dominions:
It's a fairly war focused strategy game. In something like Civ you could just settle a few cities and turtle until science victory. That isn't how Dominions is played. You recruit units and start attacking independents. Indies die, you start attacking and killing other nations. He who kills best and most efficiently tends to win.
I've seen some people get turned away due to expecting something this game isn't. This game isn't really about playing Middle Age Man and building your own little feudal empire. It's about using Middle Age Man to kill the Cthulhu, the Spanish Inquisition and the Samurai Orcs.
And yeah, there's a learning curve. Both for the interface itself as well as some basic concepts. I consider myself to 'wing it' a lot, but I've played for over a year now. Just like in music, improvisation isn't a skill for the very beginners. But worry not, it took me my first MP game to fail horribly and wrap my head around some things. Progress for me was fairly fast paced as I played and learned stuff through SP testing and MP failures (and eventual successes).
If you have any difficulties wrapping your head around things, don't be shy and ask. I'd like the think there's enough reasonably skilled and polite folks here to answer any questions you may have.