Played through Mega Man 10 again and the stage design is way better than in Mega Man 9!  I had a lot more fun with it.  However, the game does have its flaws, too, mostly the weapons being awkward to use, which also contributes to the boss fights in general being less well-designed.

A good mega man boss I think, will have two, or maybe three different attacks, and the fight should proceed at a relatively slow pace so that you can try your best to learn to navigate them.  In general Mega Man 9 I think did better at this.  Plug Man was probably the one exception as his fight is really chaotic, but Galaxy Man is a great example of how you can have a slow-paced fight where you really learn how it goes.  Splash Woman, too, has a main attack that isn't trivial to dodge, but you know it's coming and there's plenty of room in the arena to try and come up with an idea.

For Mega Man 10 I think Sheep Man had a nice fight in this style, but some of the other robot masters felt awkward or frantic to fight.  But again, I think half the issue is also with the weapons.  You've got weapons that only work well at close range (the bubble shield, the sawblade), and you've got a trio of weapons where hitting the enemy itself doesn't do proper damage (the thunder cloud, ice spike, and commando missile).  Ice spike is "ok" in that it's relatively easy to get nitro man to run over the spike that you lay, but commando missile against blade man feels pretty hectic to manage, and thunder cloud against pump man feels like a 50/50 whether it even hits.

The wily stage bosses also suffer as a result because as you're doing the dance of "try all the weapons to see which does more damage" you're getting whacked around a lot because all of the weapons are so awkward to use.

But the stages are great, and that mattered more to me.  Well-designed around core concepts that get reused.  These mechanics even show up again one after another in the wily stages, which is really nice.  The one notable exception was a few screens in the middle segment of Chill Man's stage which felt superfluous / bland, but everything else was really nice.

I played through the Mega Man 9 DLC stages as well, it was...fine I guess.  There are three DLC stages for Mega Man 10 as well...I guess I can go through them at some point perhaps, including them all is arguably the one thing that the legacy collection has going for it.