When Episode I was leaked, players were greatly disappointed at two particular levels: Casino Street Zone Act 2 was nothing but a small pinball area where you had to collect 100000 points and Lost Labyrinth Zone Act 2 was entirely focused on finicky motion controls. The game was delayed and both levels were replaced. The mobile ports still kept them, however.
Awesome Music: As a Sonic game, this is pretty much a requirement. Although some may consider Episode I's instruments to be full of a sound resembling that of dying cats, Episode II's usually don't have such sounds.
Casino Street Zone Act 2. The console version, Road of Cards, features large groups of cards that hand out items as they're flipped, meaning you can take about a dozen lives every time you play it. The mobile version of Act 2 is instead an effortless mini pinball table you have to collect points in.
White Park Zone Act 2 is an easy rollercoaster to run around, in contrast to the platfoming featured in the other acts.
Death Egg mk.II Zone Act 1 has two boss fights, but also features surprisingly simple level design you can run freely through.
Broken Base: The cancellation of Sonic 4. Some say that the project was ultimately a failure and deserved to be cancelled, as the developers ultimately failed to find what made the classic games so beloved and tried to shoehorn new gimmicks into it. Others believe that the series was unfairly evaluated and that it should have been concluded, especially with Episode II fixing much of the perceived problems of Episode I. The advent of Sonic Mania in particular has split fans on whether it was a good idea to "replace" Sonic 4.
Contested Sequel: Both fan and critic reception for both games vary when compared to previous installments.
Critical Dissonance: Many critics gave Episode I good to average reviews while most fans view it as an inferior game. Meanwhile, most critics ripped into Episode II, yet most fans consider the game to be a marked improvement over the original.
Ear Worm: This game has some too. In particular, the "Pinch" boss music in Episode I (and standard boss music in Episode II), a nearly 20-second loop of repetitive notes to the point where some people think it's shorter than it actually is. It's fine for its use as a boss theme, but it ends up being used as the EGG Station's BGM until you reach the final boss, which of course takes longer to get through than finishing off an angry end-of-the-stage boss.
Even Better Sequel: Most fans consider Episode II to be a far superior game thanks to its vastly improved graphics, less derivative level and boss design, a new physics engine that more closely resembles the Genesis games, and the ability to play as Metal Sonic.
In Episode I, you can press Retry before time runs out in the Special Stages, providing infinite attempts at each Chaos Emerald as long as you don't touch the exits.
The Rolling Combo in Episode II. Immune to almost every hazard? Check. A constantly moving Spin Attack that can take down even Snowy in one hit? Check. Makes the Stardust Speedway remake race incredibly easy? Check.
Super Sonic. This time around it's taken even further since he can no longer drown, meaning the only things that can kill him are Bottomless Pits and being crushed. In Episode I, he automatically lights up Lost Labyrinth Zone Act 2, and forces the slot machines in Casino Street Zone Act 1 to come up as jackpots. In Episode II, he's playable in boss battles and he does double damage to all bosses.
What part of the fanbase thinks of Episode I. The stages, for example, have been accused of being carbon copies of the Genesis stages instead of original stages like they actually wanted.
The general reason why Episode II received poorer reviews than Episode I. Despite the numerous improvements, most critics found the core gameplay to be not as enjoyable. Even those who hate the project overall agree that Episode II is the better of the two episodes.
Scapegoat Creator: Dimps became this after this game, after a successful run with the Sonic Advance and Sonic Rush series. With every Sonic game they have made since then, most notoriously the Nintendo 3DS version of Sonic Lost World, the games' shortcomings have been blamed on them, even though it was Sonic Team's current leader who admitted that he wanted the game to have a different feel than the Genesis games.
The camera is just a little too close to Sonic for some fans, causing them to barrel along without having enough of a view for what's headed for them.
The Homing Attack from Sonic Adventure onwards bolted onto this decidedly old school game qualifies, though most aren't really upset about lock-on dashing as they are the horizontal leap you can take when you're not even locked onto anything.
Sonic uncurling in mid-air after flying off a ramp or attacking an enemy. It's designed to force players to rely on the Homing Attack, but if they're a little too familiar with classic gameplay, they'll be shedding rings at least five times per act.
Sonic's acceleration feels significantly slower than the classic Sonic games. Good for the Scenery Porn, bad for a character who is supposed to be fast. Compare the generally faster gameplay in the classic stages of Sonic Generations.
Not being able to play as Tails outside of co-op mode in Episode II. Most stages can still be completed by having Sonic just stand there and using the Rolling Combo when needed, but some are still impossible to complete without controlling Sonic directly.
So Bad, It's Good: The intro to Oil Desert Zone Act 2's theme due to it sounding like "dying ducks" as mentioned above.
So Okay, It's Average: The general opinion on Episode I. While it's a perfectly playable game on its own, it completely fails at being a follow-up to the classic games in that its core gameplay is similar to Sonic Rush without the boost, and it tries to mask this fact by having derivative graphical designs from stages in previous Sonic games.
Surprisingly Improved Sequel: In the case of those who thought Episode I was mediocre at best. When they said they were improving Episode II, they weren't kidding: better graphics, better stage designs, better physics, the ability to use Tails as a power-up and play as him in multiplayer, more creative boss fights, Red Rings, small nods to older games, and Episode Metal, to name a few.
That One Achievement: In the Xbox 360 version of Episode I, you get an avatar award for collecting all of the rings in the pre-credits area. What makes this annoying is that Sonic moves on his own, so you're done if you miss any, and if you don't get it, you have to finish the final stage all over again just for another shot at it.
The Special Stages in Episode I. It has the most complex design and a ton of bumpers next to the exits. The low time limit doesn't help matters. The physics are odd as well: Sonic bounces when hitting walls and when grounded on them, he sticks too much, which results in very imprecise, time-wasting controls.
True toDimps tradition, the Special Stages in Episode II range from easy to somewhat difficult until you get to the last one, which is nearly impossible.
Sky Fortress Zone Act 3 in Episode II can be difficult for some, especially for badly coordinated players in 2-Player mode.
They Changed It, Now It Sucks: Some of the issues the games have been criticized about includes the use of Sonic's modern design in a sequel to the classic-style games, Eggman not being called Robotnik, the over-reliance on the Homing Attack, and the physics.