On the one hand, Sonic 2 is a wonderful platformer with lots of redeeming characteristics: it has the best art work in the series; it has the best music of the Genesis entries; and many iconic series staples, such as Tales and his biplane, and a Robotnik airship, were adroitly introduced therein.
On the other hand and from a pure design perspective, Sonic 2 has a number of issues-- problems which either did not manifest in the original, or which were actually strengths of the first title, marking a notable regression in the use of sound design principles. Here are just a few, off the top of my head:
- Pacing: Sonic 2's initial levels-- with their plethora of lamp posts, ready availability of rings, and open layouts-- actively encourage the player to collect as many Chaos Emeralds as possible. The outcome is that the first part of each playthrough is plodding. I've had people passionately defend the game by humorously suggesting that I ignore the lamppost stars-- which is not an argument in defense of the game's design, but rather a way of working around the poor design-- a way which is also inadvertently admissive of this shortcoming in the game's construction.
Once Super Sonic is available, the game has the opposite issue, in that the levels can be veritably flown through-- during which the boss fights become hilariously trivial, and it becomes dreadfully apparent that the stages were not designed with Super Sonic's speed or increased jumping height in mind. Notably, this was somewhat remedied in Sonic 3, where opting in to Super Sonic was optional for the player, since it required consecutive button presses, versus a mere single jump. - Lack of Tempo: In the very best platformers, there is a sort of "rhythm" to the gameplay. Watching a skillful player swing his way almost melodically through the first title's "Green Hill Zone"-- or almost any of the rest of that game-- is a text book case.
In Sonic 2 however, the designers went away from the methodical and water-tight stage designs, opting instead for sprawling, multi-pathed levels. Like a chess player attending to several matches at once, their attention was clearly divided, and the game did not receive the level of attention to object placement than the first title most definitely did.
From this same vantage point, many of the enemies are poorly designed in that they seem implemented with the express purpose of disrupting the game's flow. This can been seen as early as the game's very first stage, which features monkeys that, if leaped at immediately, cause the player to get hit by a coconut. Instead, the player has to stand beneath them, come to a nearly full-stop, and hit them from underneath. - Cheap Shots: One of the core "game design 101" principles is to expose threats to the player in a way that the player can reasonably react. In Sonic 2, this principle is violated frequently, especially in the later stages of the game. I took down a note of one part in the "Metropolis" zone where it is quite literally impossible to ascend a yellow-arrow spring shaft without getting blindly hit by a mantis at the top. And if that happens, the mantis walks to the edge, totally paralyzing the player's progress through the stage!
That's not to mention the infuriatingly designed and placed crab baddies in that same set of stages. Or the "unavoidably hit out of the blue" seahorse enemies contained within "Oil Ocean Zone", which happens to be-- in part due to these very seahorse baddies-- the worst zone to appear in any of the four Genesis titles.
My operating theory-- and unlike the above, I can't "prove" this, but I'll introduce the notion anyway-- on why Sonic 2 is often held up as the best title in the series is because a significant chunk of the Genesis' lifetime sales occurred after the price drop which also saw Sonic 2 become the pack-in title.
Ten year-olds-- ill-versed in game design principles-- who excitedly had this very fun (albeit somewhat flawed, as discussed above) graphical tour-de-force to show off to their friends, as the very first game for their sparkling new system... of course they will reflect on it with immense and understandable fondness!
Perhaps they then went back and played the first game, after the fact, and being only able to judge on the most superficial of characteristics, were struck by the game's somewhat muted-by-comparison aesthetic, and the lack of the "spin dash" move (although there isn't a single moment in the first game where it's of particular use anyway)... and that, thus, is from where the ill-conceived notions were first given life, and were never thereafter dispelled (except perhaps by this very blog post).
As for me, I had a sizable Genesis library before "Sonic the Hedgehog" was even part of this universe. And so, I bought the first title... and the second game... and the third entry... and "Knuckles"... each on their respective "day one" release dates. So, I don't hold any particular nostalgic favoritism for any one of them at the expense of the others-- I played, memorized, and loved them all, as they came out.
And I continued to play and love them continuously from that bygone era, all the way up to the present, objectively applying my ever-increasing game design insight to their designs-- leading to blog posts such as this.