Ah, I love this thread.
The Dutch-Belgian army was a real late-Napoleonic one - Almost all of those who had experience, had been fighting for the French. The fact that their regiments had deserted the French en-masse in 13/14 didn't stop British suspicion towards them.
What can we say about the Regiments? Trough the research of army lists, it has been discovered that the amount of deserters was actually quite high, but many of those deserted just before a battle (Bit scary after all) or after the (first) abdication of Napoleon. Many has signed 3 or 6 years of service, and they did not particular wanted to serve another 5 years in fortress service.
One other fact is that this army was largely made up of volunteers with no experience - the Dutch army, which had been re-organized many times during the Nap. Wars, was always made of the same men - But those men had mostly died in Russia. I estimate that about 1 in 5 of every Dutch-Belgian soldier of the regular army had been in the army before.
Now let's look at the battles. First, Quatre-Bras. Against Wellington's orders, The Prince of Orange decided to deploy his corps alongside the crossroads - Saxen-Weimar in the woods, with some companies of the 27ste Jagers, and the 5th Battalion of Militia in Gemincourt farm (Both battalions were part of Bylandts Brigade, which also included the 7th (Belgian) Infantry battalion.). They skirmishes for the entire morning and a part of the afternoon (Unlike Sharpe's Waterloo, where nothing happens, until the British heroically arrive. God, I hate that book.).
Eventually, Ney organised an entire French Brigade to attack Gemincourt farm. They threw out the 5th, which reorganized at the north. At that time, the 28th Foot (British) came marching down, but as they saw the farm being taken, they retreated. The 5th Militia, however, thought they were going to be re-enforced and charged the farm, clearing away the French soldiers from everything except a farmhouse. They then deployed SOUTH of the farm, and managed to kick back three cavalry charges, being lead by the Prince. There has also been an account of a dutch horse artillery battery which recaptured their cannons by a sword charge - Not bad for men who never received proper cavalry training.
Though, some stupid things happened too. The 27ste was caught in line by the Red Lancers and suffered heavy casualties, and a cavalry charge made by NL cavalry was, all trough successful at the start, pushed back and fired upon by mistake by the Gordon Highlanders. At a certain point in the afternoon, Wellington took command and with him, a large British continent took over the battle from their tired Dutch allies. We can just guess what happened if the Prince had followed Wellesley orders to keep retreating - It might have made sure the Prussians and British-Dutch army were split long enough for Napoleon to win Waterloo.
At Waterloo, Chassé's Division, of 2 Dutch brigades, was deployed to the east of the battle, to stop the flanking attack of Napoleon - Which never happened. The Bylandt Brigade (here they are again!) was deployed before the ridge, and thus in perfect range of French artillery. God knows why they were still out there. Some say Wellington placed them there just because he didn't care about them. Personally, I think it was just a mistake, made by multiple people. Anyhow, the Brigade took heavy casualties and was the first to be attacked by D'Erlon. They made a most gallant stand, according to some 92nd Highlander officers. According to 'historian' Siborne, who wasn't there, they ran without firing a shot. Choose who to believe.
Late in the afternoon, Wellington knew there was a final attack coming, and so he ordered Chassé to deploy his division to the west of the British line. He marched them quickly behind the British line, as the French Guard was attack. The middle Guard was leading this attack, which wasn't directed to go straight at the, but from east-to-west. Chassé deployed one Dutch brigade as general reserve, and another one, Detmars, marched into position just as the Middle guard was reaching the slope of the hill. They shot them to pieces, and cheering they made a bayonet charge (Chassé was also known as Generaal Bajonet - he favoured the charge) and they drove them back. But instead of holding their position, they went after them, 10 to 15 minutes PRIOR to the famous 'General advance'. Trapped between La haye Sainte and the Dutch brigade (which consisted of just two battalions of regulars and four of Militia), they put up a good fight, but ran eventually.
And here I end my story. Yes, I sound a bit biased for the Dutch, that might be, but I believe every word I said here, and I got direct evidence for most of it.
Oh, another fun fact - one of the corporals of the
6th 2nd (Dutch) Infantry battalion, part of Detmars brigade, was Czech, native of Prague.