I've got a lot of different things I want to say about this game, but a big generalized text dump doesn't feel like the right way to go about it. Therefore, I'm going to try and spread them out across a series of level reviews. This is mostly for my own benefit, but feel free to chime in.
Green Hill has been revisited, rebuilt, referenced, and paid homage a dozen times over and more. It's probably the second most iconic level in video games behind SMB's 1-1. Generations couldn't
not include it.
Level Design
Bleeeeeeh. Act 1 is a tutorial level, and it's a
boring tutorial level.
Where the original at least had the good grace to require some careful platforming up top and lined the bottom with spikes and badniks, Generations removes all semblance of difficulty entirely. The badniks themselves are completely ineffectual as hazards; Choppers are almost nonexistent, Buzz Bombers and Crabmeats have ridiculous delays before they attack, and Newtrons got axed entirely. The need for platforming in general is heavily reduced; I've managed to complete the level with just four jumps, and it might be possible to go lower. There are a couple of routes, but the top is largely flat and featureless while the bottom is so loaded with springs that it largely plays itself. Several of Emerald Hill's distinguishing features are present, and a couple of weird curves bring to mind modern day DIMPS more than anything.
There's also quite a bit of obvious scripting going on between the various ramps, springs, and loops that hamper player freedom. The loops in particular are a bit shoddy and tend to break if you look at them funny.
On the whole it's dull to play, missing both the intricacies that made the original GHZ memorable and the unique gimmicks that define most other zones in the series. It didn't need to be a perfect recreation of the zone, but it's missing a strong identity.
Art
Where the level designer didn't get it, the artists did. GHZ has never looked so good, from the towering cliffs to the enormous totems to the gorgeous new cave environment. They may have tried to make it
too grandiose; there's been plenty of talk about how small Sonic seems compared to the environment, and it's true. Upward ramps and loops are especially enormous and further serve to highlight the game's problems with maintaining momentum. Even the stripes in the grass and checkerboard pattern in the dirt have been scaled up.
The most thoroughly reimagined asset is the background, which has morphed from two parallax layers of indistinct mountains in the distance to a sprawling array of cliffs much like what comprises the level itself. They're a bit close, though, and you can't often get a good view of the water and distant mountain layer as in the original, which changes the zone's atmosphere somewhat. The sky, when you can get a good look at it, appears to be made up of real world photographs and seems out of place.
Music
All of the classic mixes of classic zones stick close to the original sound, and that's for the best. The drums and bass were completely redone, and lots of little subtle synths were added into the background in a way that reminds me of Angel Island Zone. The result is a solid remastering that updates the tune without straying into Sonic 4's wretched faux-retro sound. It loops weirdly, though, going through the intro again for no apparent reason.
Level Design
Welcome to Straight Line Zone. It's the tutorial stage and modern Sonic has a fairly complicated control scheme to get used to compared to classic, but it's embarrassing just how linear this level is. And if that weren't bad enough, it's all but devoid of anything to actually do. 3D sections are very nearly platforming-free and mostly consist of boosting through helpless rows of badniks. 2D sections at least have high and low paths, though both are as simple as it gets. Either path will at least require you to jump more than you do in Act 1, which is something.
While Act 1 incorporated a few of the mechanics and design elements that distinguished GHZ from other zones, Act 2 doesn't even try. Its one nod to its origins is the standard crumbling platform, which tends to be attached to otherwise solid ground as in the original. Every other mechanic is entirely generic, though I believe the bridge stomp near the end is the only such occurrence in 3D.
Perhaps it's for the best that there's so little similarity, though. Modern Sonic bears effectively no resemblance to Sonic 1, and Act 1 already proved that doing things halfway only ends up feeling vaguely awkward. It'd be a terribly bland level without the art, though, and even that can't completely save it.
Art
If Unleashed taught us anything, it's that blasting through 3D environments at the speed of sound is a great visual rush. The stages in that game were a bit drab on the whole, though, their real world origins struggling to be truly distinctive. Enter Green Hill Zone, the most visually iconic stage in the entire franchise. The match between the two is breathtaking. The immense scale of the art makes sense here, as modern Sonic tears past even the grandest set pieces in the blink of an eye. The ocean views that felt absent in Act 1 are out in force in Act 2, accompanied by screen-filling waterfalls, another eye-catching cavern section, and some particularly nice shallow water paths near the end. The new wooden plank platforms seen in Act 1 get more use here and help this take on Green Hill have a distinct feel from the interpretations that came before it.
Music
Modern Sonic, modern instrumentation. Senoue's signature guitar and a brass section play harmony, but the lead is further proof that the man can't choose a decent synth to save his life. It isn't Sonic 4 bad, but it's still an annoying, whiny sound that doesn't mix well with the rest of the piece. After a couple loops it shifts into an odd offbeat version of the melody that wasn't necessary at all.
GHZ is one of only two zones to get a high speed version of the track that kicks in when you're really blazing along, and appropriately it punches up the intensity. There's an extra guitar track added, and the drumming punches it up to the most frenetic speeds you'll hear this side of Unleashed. It's a nifty touch, which makes it that much more of a shame that more levels don't do it.