I was initially a bit deflated playing Scotland on vh/vh and winning relatively easily. But I started a vh/vh campaign as Russia yesterday and I echo everything PaulTa said. Here's a brief outline so far:

Initially start with a single province surrounded by rebels. I grabbed neighboring Helsinki, Smolensk, Vilnius and I was headed to capture Moscow and Ryazan when Poland attacks. Fighting Poland is brutal as none of the my newly captured provinces was developing much revenue and money was very tight. I had to check my Eastern expansion for about 20 turns. When I have Poland fought to a standstill I finally grab Moscow but now Hungary is headed into the steppe territories and had taken Kiev and Ryazan. Big distances between my cities in this part of the map. Very hard to fight on two fronts so I'm much relieved when Hungary agrees to alliance and I can concentrate on Poland.

Basically I then fought Poland tooth and nail for about 30 turns finally taking Riga and Thorn from them. Just as I'm beating them with some better units Denmark attacks. Denmark has a slew of good units from crusading. Now another 20 turns of brutal warfare against a weakened Poland and a strong Denmark. Denmark owns the Baltic Sea so I cant do much with the Navy or trade. Trying desperately to build my economy and trade through other means.

The war is great. I had several battles where it came down to a few units on each side and a half baked charge in the rear by a returning weak unit remnant like missile cav was enough to end it. I lost a few that way and won a few. Unit experience and upgrading the Generals is critical. Noticable difference fighting those blood and guts last stand battles with lower experience units - inexperienced generals often get hammered. Almost never use autoresolve. Probably winning better than 75% of battles against the AI through planning my army unit composition, using best generals and picking best battlefield site. I never have more than about 2500 florins each turn except after a couple of sackings when I have money to upgrade the cities and castles. I am never flush and use the money carefully to recruit maybe 5 or 6 units max per turn.

A couple of turns after I focussed on Denmark and Poland has switched strategies and attacks with armies of good cav units and more missile units and stops using militia. Now of course my merc crossbowmen are useless and I really need my castles upgraded to get better units. I'm able to create a 3 way alliance with Hungary and Venice so I don't worry so much about my southern flank and the East. God help me when the Mongols come....

If I had one crushing defeat and lost an army with a good general I would lose the campaign. It is that close. I haven't had to deal with an AI that gets crazy economics and can hammer me no matter what I do - instead I'm having to deal with AI that is actually upgrading, picking good units to match my choices. I'm using river crossings to choke AI movement, ambushes, high ground, sometimes have to retreat to avoid being surrounded as Denmark has at least double my strength.

In short I am having to think every turn about how to use limited resources to best effect. I'm using all the strategic elements of the campaign game and barely hanging in the game. I'm not being spammed with stacks of cheap AI units. The AI is using the same game elements as me to try to win. It's a joy to play this game. I must have sat at the computer 8 hours absorbed with it. I'm sure a month from now I will find it a lot easier but at the moment the AI and I are well balanced in this campaign.

Kudos to the developers. This is what strategy gaming is meant to be about.