Compare one of the best levels in classic sonic to maybe the worst level in Sonic 4?
Lets compare Green Hill zone from Sonic 1 to Splash Hill Zone...
Green hill zone is pretty flat and boring, it's short and has no gimmicks so to speak... The first act of most Sonic games have been pretty dull design wise. Sonic and Knuckles was the exception to the rule.
Green hill zone act one has 1 loop to its name, while Splash hill zone has mutlipe loops, zip lines, vine swings and so on. Making it, in my mind... A more fleshed out level.
The only thing I would change in Splash Hill is the mid level background. Those bushes look a bit crap but the far off background looks good.
Why would you do that? It is like saying if Nintendo makes a new 2D Mario platformer with poor level design and gimmicks that it is okay to compare to the first ever 2D Mario platformer. It is not, they should try to improve. At the time Sonic 1 came out, loops and even bridges that bent were considered gimmicks themselves.
But if you want me to prove Green Hill Zone is much better than Splash Hill Zone, I would be very happy to!
First off, Sonic the Hedgehog only had two zones with loops in it at all. Not that it would matter as they do not add much to the game outside of an extra platform above them. Wacky Workbench from Sonic CD has more loops than any 2D Sonic level, and is one of the worst level in the series. The two loops in Green Hill Zone are nice in that to get on top of one you need to get past it first, then go backwards and roll, then jump off of the wall to reach the platform above it, there is no other way to. This alone requires more skill and thinking than anything I have seen in Sonic the Hedgehog 4, period.
Next, go back and play the Zone again. I will give you that they are short, but at the time this was the most expansive level in a platformer to date, only being rivaled by Super Mario Brothers 3. You could go in all different directions, which would lead to different items and paths. You could go through high-speed tubes, there was a spinning pointy log bridge, there were cliff edges that would break. All of this is not really impressive now, but my point is that a big game made in 2010 should be at least slightly better than a big game made in 1991, especially when there are much more impressive design concept added into the series within those 19 years.
I could go on for hours about what is wrong with the art design in Sonic the Hedgehog 4, but I will not. I just want to say that even stuff like Sonic Advance, Sonic Triple Trouble and even Sonic 3D Blast has better level art design and gimmicks than Sonic the Hedgehog 4 does, and I do not think this is acceptable at all.