They are good early on In the lower HC levels but as you move up past Level 14 They start to get weaker and more frustrating, as other civs get cards that essentially wipe out the dutch unique advantages the dutch don't necessarily get cards that improve them much other then merc cards that are rather expensive and eco shipments Food/gold that don't help much.
In the lower HC levels you can push and rush early with Skirms quite effectively, even hit age II as fast or faster then Ottos and get a hefty military out. Or turtle and boom past your opponents.
In upper Hc Your kind of forced into the slow death Turtle/boom. Since other Civs can Now use hefty food/gold cards. That make your supposedly better economy less of a fator, plus they get better military cards. Gold costing Villies become a hinderance rather than asset since, aging and all dutch worthwhile units cost gold with the exception of pikes wich you probably won't use that much except a few to counter uhlan, hussar raids early.
Skirms are'nt that great when up against massed forces Wich are easier to aquire in the Higer Hc levels even if you have an equal or greater number of skirms. Skirms are great with micro but tthere fire rate is to slow compared to other cheaper units such as archers, long bows and jans once two massed armies meet microing makes things worse and without micro they tended to lose. The dutch don't have any other effective ranged units such as archers or muskest that they could mix in there to balance things out. And never Group slow units in with your skirm it will slow them down ab certain death.
They do get the ruyter but you will quickly realize that they are not that great and the pop/resources are better spent elswhere. They make a good counter cav but like the skirms require focus fire and micro to take advantage. So the more units you have and more units you go against they become less effective.
Even if you manage to get banks down early, wich are very expensive you will still need to have quite a few Villies on gold if you plan to age, keep villies pumping, and have a military.
So you will love them early on and slowly but surely find yourslef having a harder time as your unique advantages start to whane in the higher Hc levels.
And finally the dutch really have a problem with anti Artillary, no good counters to it since the bulk of your army will ranged. And artillary cost so much gold that its hard to afford it along with your army.
The Dutch are my fav civ so far despite all that just because they are the only ones that actually require any real micro thanks to the second age Skirms. More Units in AOE3 should be moddeled after skirms (meaning that you actually have to do something with them to be effective, rather then just spamming units and leading them to battle like all the other military units outthere) But i have been using other civs, more and more just cause it's easier to win. Less fun but i get lazy sometimes.
Anyway this post is a linttle winded but i caught on my lunch hour. S0 :-)~