Well the bayonet as a melee weapon is nothing really out of the ordinary, it is exactly as effective as a spear of the same length would be, there's really nothing else to it, it's just a stick with a sharp blade on its end, so of course it has greater reach than a sword but less reach than a pike. Bayonets and pikes were indeed used together during the late 17th and early 18th century before the bayonet completely took over the role of the pike, the swedish in particular are well known to have retained the pike after other powers had abandoned it due to their aggresive tactical doctrine that relied far more on cold steel than on firepower. Cavalry still used swords and would cut down infantry formations if it managed to break through any gaps or attack the flanks or rear, but infantry could arrange itself in a square formation to present nothing but bayonets against the incoming cavalry, with no weak spots; Lancers had a better chance due to their greater reach, but still had to fight against a much more densely packed enemy which made headway difficult.

But of course the bayonet as a melee weapon is not really what makes it special is it? It's the musket as a melee weapon what makes a difference, and from the point of view of the question, a musket with bayonet is a spear with the added capability of being able to shoot a lead ball out of its shaft at way past the speed of sound, which in most situations is strictly better than having a spear that can't do that. This duality of having both melee and ranged capabilities is what makes the 18th century flintlock musketeer so effective and versatile, as he is able to provide firepower to disrupt the enemy formation as well as being able to break it up with a bayonet charge, all without having to sacrifice firepower to specialized heavy infantry nor staying power to specialized light infantry. The musketeer was of course not particularly adept at close combat, lacking armor for reassurance and never with the best morale, almost always a succesful bayonet charge was an uneventful one, as a formation would wither away and flee when faced with a determined enemy that approached undisturbed by musket fire, so actual melee in the battlefield was rare, it was more common to see it when fighting in villages, redoubts, trenches or other forms of field fortification, in which close quarters were a given. The musketeer was also not often the best at providing the most effective fire, as they tended to shoot at the enemy way outside effective range (which might make your fire harmless, but the enemy's fire too!) and hardly bothered with aiming the weapon, just scrambling to load and fire as quickly as possible; the tactics of the day emphasized orderly, coordinated firing by ranks or by platoons, but that was the ideal that was sought to be achieved, while the reality often devolved into uncoordinated firing at will. So the musketeer worked as a sort of jack of all trades master of none, but that arrangement was very effective, for he was able to defend against enemy charges and charge on his own with his bayonet, or overpower the enemy with musket fire, while the previous arrangement of pike and shot (or even earlier arrangements like archers and men-at-arms) could only do one or the other