I played P&M for a few months, although the invisible and faulty units really began to annoy me.

I would suggest playing on the campaign which has the most factions on the map, (Not the Sun King's Ambiton or Religious Turmoil), for then there will be less chance of three major factions destroying everything else right from the beginning.

I really liked the mod for it's progress in technology, but it also had a few faults - I never enjoyed holding of waves of town militia, who were actually just floating, shape-shifting blobs.

But you have only just begun!

I remember the fun I had in my French campaign, in which I swore to protect the meek factions and destroy the Spanish, Ottomans, and Russians.

Please, tell us more here about your future campaigns!