Outside of about 5 major issues I have with sonic 4 I think the game is ok, but I am not changing my mind any time soon because of 5 classic sonic breaking reasons:
1) Rolling is borked, Sonic's roll doesn't work anywhere near the same as the 16bit sonic's, hell, even sonic adventure has a better roll then sonic 4 and that was a fucking dreamcast launch title! in SA1 I can roll down hills and around loops and go fast while in a ball, and launch off ledges maintaining sonic's ball form. Rolling is important to a 2d sonic game because you trade things like air control (jumping out of a roll takes away sonic's air control )and the ability to brake and slow down for a better and faster top speed, being able to attack badniks and launch off a ramp for more height.
2) Uncurling, this also breaks rolling because you are forced out of a ball into a vulnerable state just so you can abuse the homing attack, it's stupid and silly for a 2d sonic game to have uncurling like sonic 4.
3) Boost pads are way overused, if you go and look back at the classic games only a few choice zones had boosters to help you around loops or over a long stretch of layout, chemical plant for example. In that zone there was only about 6 areas where you really went flat out and because of that it felt great having a quick burst of speed and 4 loops to run through before going back to a slower platforming route, it was a luxury and thrill to have that speed only for a few seconds, sonic 4 slaps this up constantly. The classic games would use side facing springs or expect you to roll down a hill before the speed trap.
4) Forced homing attack, the closest we had in the classics were the flame shield and sonic 3d's red shield which was important because of the whole isometric angle made it tricky to sometimes hit an enemy. Instead of sonic gaining homing attacks out of the blue it would have been better to give it via a shield, if you lost that shield before a homing segment then you have to take the default route instead of the homing bridge one, which could have rewarded the player with more rings and an extra life, something else which is overly-plentiful in sonic 4.
5) Floaty jumping with a terrible pointless X-axis momentum stop when you let go of a direction, it's not the worst problem out of the 5 but it's still stupid, this isn't a 3d title where you sometimes needed to press B and land on a tiny platform, classic sonic's never had a problem with tricky jumps, never, why bring in stupid jumping rules when they were not required? Launching out of a cannon without holding a direction will stop you dead at peak and you will drop like a brick, not cool.
Other minor things which are just visual are things like ring splash (too weak in sonic 4) and the spindash sound effect not becoming higher pitch which means when you rev you get a spam of the same sample overlapping each other until your ears bleed, pitch change helps that problem a lot and it lets you hear how fast sonic will launch at.
Do I expect any of this to get fixed for ep2? a few things might be tweaked but I can't see it happening, it would break any kind of lock-on and I fully expect sega are going that route, the map screen kind of gives it away on the right hand side and with the next ep possibly giving us tails, i'd expect him to be playable in ep1 stages too. Sega should have made episode 1 as good as they were able to but failed over just a few things, if only they spent the last 3 months actually fixing the game instead of adding a map screen and animated title, oh and two replacement acts which just use the already broken dimps physics a little better then the other stages.