Four games, three distinct visual styles. Mega Man Legacy Collection 2 may feature representatives from three eras of console gaming, though that's not immediately apparent unless you've kept up with the series the whole way through.
Mega Man 7, being a Super Nintendo game, looks every bit the part. There's a complexity and softness to the sprites that is classically 16-bit, and while its level theming is lacking in parts, it's consistent throughout. Good stuff.
Mega Man 8 introduced anime-style cutscenes, but the in-game field of view appears greatly expanded. 7 may feel a bit too close for comfort at times, but by comparison, 8 looks zoomed out. It ultimately works, though the enhanced graphics made possible by the Sony PlayStation resulted in a game that's way too busy for its own good.
Mega Man 9 and Mega Man 10 mark a return to the 8-bit visuals that were made famous by the six Nintendo Entertainment System classics. Whether the assets are new or recycled, they make for a charming aesthetic.
In terms of sound design, each game represents what its generation was trying to accomplish in the context of the franchise as a whole.
Mega Man 7 reintroduced the classic cues of the originals, but utilized the expanded palette of instruments allowed by the SNES to deliver something more memorable.
Mega Man 8 is famous for its sound design. By "famous," I mean "infamous." This is primarily due to the performances in the English dub, which are uniformly, spectacularly bad. Mega Man sounds like a little girl, and Dr. Light is what you'd get if Elmer Fudd, against type, decided to play it straight. It's a beautiful disaster, and easily the most entertaining aspect of the PlayStation original.
Mega Man 9 and Mega Man 10, in a manner befitting their retrograde visuals, boast complex, catchy chiptune soundtracks that perfectly evoke what it was to be a Capcom soundtrack in the late 1980's and early 1990's. The same goes for sound effects, which are, part and parcel, exactly as they were for the original six.