Rant ahead. Warning. Long.
Initial thoughts were that DSZ was completely boring, and had far too underwater areas. I now revoke this statement (now that I've completed, and just replaying to explore and find all the emblems).
However, more air bubbles and springs should be added. Really, single air bubbles in massive water areas is silly, because they're practically invisible. Springs mainly for Sonic. Act 1 is a bit too puzzly and finicky (namely with Sonic) too; it's fun, but really slow as a level. With the exception of the water slides. Those were fun. Really, really fun.
New-CEZ was far more navigatible. I didn't get lost, and after the almost turtle-paced (in areas) DSZ, this was excellent. The almost overuse of spikeballs in act 2 is really bad though. The twirling ones are alright, but the side-to-side ones are extremely hard to dodge.
ACZ and RCZ were fun. Obviously need second acts, but still good. I don't know whether it was the lack of a second act or not, but they both seemed a bit easier than the predecessors. Still amazing though.
ACZ's gimmicks were very fun, even though the wires seem quite hard to grab on to successfully. There was also some minor navigation issues, as I ended up going in circles for a brief period. I didn't get lost nearly as bad as I did in DSZ though.
RCZ was fantastic through and through, and the elements it set up for the final zone were great. It's quite a shame the second act for this one wasn't finished for release; considering that Act 1 was at least partially present in 1.08 (albeit, y'know, unfinished).
DCZ wasn't there. Given the difficultly jump between RCZ and ERZ, will it be completed for the final version? Considering all of the new features, it seems hard to imagine what sort of level this'd be, really.
DSZ? Scrapped? Seems like ERZ kidnapped anything that it could've been anyway.
ERZ. Wow. Unlike DSZ, which had me quitting in frustration, this just got me hooked. I must've died over 100 times. It was difficult. But, so, so fun. Act 1's easy now; I can do it with no deaths, and usually 2+ more lives. Act 2 was really (really) hard, but completely epic. It was amazing. I laughed, I cried, I think it was the most fun I've had in a Sonic game, ever.
Make that in any game ever. I have never had so much fun playing a game.
The length of it was astounding too. I think it more than makes up for the removal of Doomship Zone; I couldn't imagine how a level like that could differ from this one, anyways.
I must admit, to complete it, I did have to abuse a certain spawn point for extra lives. The first time, I ended on about 50 lives, and proceeded to waste 40 of them trying to figure out how the hell to do the boss.
Second time round, my 100 lives dwindled down to 50, as I finally beat the boss, and figured out how to beat him post hit six. It was so unexpected; that is, the ways to beat him. It was utterly brilliant. And an awesome Sonic OVA reference. I certainly flipped him off throughout the whole experience.
The Special Stages were... there. I dunno. The wiki says they're being replaced with NiGHTs-esque stages? Cool? I don't really care, Super's not my thing.
Other aspects. Some areas seemed really pointless, like "wow, decoration!". It'd be nice if some of the elusive, non-emblem and pretty pointless areas were given some sort of secret tag, ala, what other than... Doom?
Graphics were fantastic. What else is there to say? Although there was a tad bit of texture blandness in a few levels, the level design itself was detailed enough to more-than make up for it. The enemies (redrawn included) looked great.
In terms of this, ERZ was just awe-inspiring. Creative uses of textures, and great textures at that. A lot of work has obviously been put in.
Depth-perception hurt a few bits, such as Arid Canyon's wires (not so much) and Castle Eggman's spikeballs. For the spikeballs at least. perhaps if they were given sprites at different angles, showing different spike positions or something, perhaps it would help slightly. Or maybe if they were made slightly smaller?
I agree with most of the negative comments about the archer enemy; needs an attacking frame. I like it though. All of the enemies were fantastic, anyways, with the pain-in-the-ass mole Badniks to the newly redrawn Eggmen and Crawlas. The early flying enemies sort of still suck hard though. They just look a bit, well, too goddamn small.
There were some glitches present, but bar the rare sigsevgs in ERZ2 (and once in ERZ1, I think), and the wide-ranged rotating spikeball of sigsegv in CEZ2, nothing gamebreaking.
With all that said and done. What I've found and played so far as been incredible on the whole, and the exploration post-game (and to find emblems) is really quite fun. I've not really messed with Match yet, but the changes look promising.
Dissapointing? Hell no. Fun as hell? Yes. Could be improved? Excepting the unseen, DSZ (especially) and CEZ (Act 2, mainly) could do with some touching up. ERZ was perfect, bar the rare random sigsegv.