Unless I decide to join/host a netgame in the near future, I will not rate multiplayer maps. Coincidentally enough, though, I seem to have rated nearly half of the maps anyway. Well, whatever.
Single Player
Elemental Mansion Zone: Act 1 - 9/10
To call this a mansion is an extreme understatement. While graphically bland in spots, the size and complexity of this map makes it surprising that I never got lost and inadvertently backtracked. This map not only contains several familiar SRB2 elements, but a multitude of gimmicks and an innumerable amount of secrets and easter eggs for the player to look for. Every playthrough brings newer discoveries, and playing the map with all three characters proves equally enjoyable. I am personally impressed by the dynamic nature of some of the map's level design as well as gimmicks that I have yet to see in many (or any) maps. A few touchups could possibly be done here or there (I think I spotted a missing texture, but there's no way I'd be able to find it again), but otherwise, this map is quite stellar.
Arid Oasis Zone - 6/10
Uncertain about this zone's status of qualification in the contest, but I'll post my review nevertheless.
This, oxymoronically enough, lives up to its name; it's a desert, but there's plants and other scenery all around the place. Seems like just the thing that would fit in a 2D Mario level such as this, and it looks quite gorgeous. As for actual gameplay, the level is appealing on the first run-through, but while it contains a couple bonus rooms, it otherwise has no alternative paths, so, paired with the fact that this level is short, the lack of replay value this map has creates no lasting effect on the player in terms of gameplay experience. This map could have been compatible with ShufflarB2, but sadly, it isn't, so this map is forcefully cursed by SRB2's default shoddy 2D system. In the map's defense, however, this map is otherwise very nice. It's a lot more eye candy than many of the other 2D maps I've seen (give or a take a sliver of OpenGL redwall), and gimmicks such as the background Jettysyn gunners make this enjoyable to play at least once or twice and memorable for ten minutes.
Limestone Ruin Zone: Act 1 - 6/10
A DSZ-themed map, which shouldn't be confused with Limestone Lake Zone. They are two very different zones, as I've experienced.
I was amused to be greeted by two bouncing gargoyles in the background at the beginning of the level. Personally, I felt the level design was pretty solid. There are plenty of paths that branch out from the main ones, and it's still particularly easy to know where you're supposed to go. There are a few creative gimmicks that work pretty well in this map, such as the line of turrets/skims, as well as the waterfall path. After playing twice, though, the zone doesn't seem to stick out in my mind much. The rest of the map is fairly generic, and suffers from the unexpected bottomless pit syndrome in certain places. Then there's the fact that in specific places, I hear a whole bunch of skims dropping bombs when I'm nowhere near them. Creepy.
Techno Meadows Zone - 2/10
Techno Hill Zone was better off wearing a condom when screwing Greenflower Zone. Its bastard child, Techno Meadows, suffers from a severely unfavorable mixture of differently themed textures, awkward grass edges on one side and none on the other, and various AFALLs in certain pits. Not to mention one wall that seems to be scrolling extremely fast for whatever reason in a... erm, "factory" part of the level. Even if Techno Meadows was graphically fine, it still suffers from an overall flat nature, along with randomly placed bottomless pits and pits of water/slime, in which the liquid is usually to-the-frac-unit equal height to the ground. At times, there are either no enemies whatsoever, or a pack of Crawla Commanders that produce such a tense battle that all I have to do is hold the spindash button for thirty seconds to defeat them. Near the end, there are also diagonal-upwards red springs that should propel you over a large bottomless pit... but unless you steer your self, you hit a wall and die. I realize there was... well, a miniscule amount of effort that was put into the level, so I gave it one more point above the minimum.
Limestone Lake Zone - 4/10
Limestone Lake Zone takes place on a riverbed as well as a cave that... apparently contains toxic water? Technically, the map contains no errors, but there are several issues contained within the wad itself. The first thing I noticed was the custom music, which... sounded strangely pleasing at first. As time went on, the tune just became more and more annoying to listen to. There are also far too many plants in the center of the platforms that it ends up blinding my view of enemies and, in first person mode, terrain. The map appears to have some nonlinearity, but the way some paths just kind of bridge randomly makes it extremely easy to get lost, especially if the player is peacefully cruising in the air as Tails -- as a matter of fact, the level is actually quite short, but if you get lost, this level may take you about three or four minutes to get through. For reasons unknown, every here and there will be a random brown rock texture within an extremely shallow cave that I thought could be spindashed through, or a railroad that blacks into nothingness but might be a secret area; attempting to explore such sights of interest leads no results. This map is nearly featureless with the exception of a few shield monitors, and those aren't hard to find.
Magma Core Zone - 6/10
This zone is mostly set at a volcanic theme, though there are industrial elements that are fairly noticeable throughout the zone -- suitably, the custom music in this map is Lava Reef Zone: Act 1; it would seem more professional (and take up less filesize), however, if it were looppointed. This map is set at a pretty medium difficulty, leaning toward hard. This is also emphasized through the use of thing type difficulty settings -- in hard mode, you'll notice this immediately when you come across the turret near the beginning of the level. The level does make nice use of gimmicks such as continuously falling rocks as well as lava falls, but Sonic is fatefully crippled at the second or third checkpoint (my memory fails me), as one path contains an area that a character must ascend, which Sonic can't seem to do very well. Taking the alternative path activates rising lava. However, Sonic is once again cornered with his inability to fly, and Sonic succumbs to the lava every time he attempts the path. This unfair disadvantage Sonic has makes it seemingly impossible for him to complete the level. Tails and Knuckles, on the other hand, can easily succeed where Sonic struggled. The rest of the map has no real problems, but people who play as Sonic will be left clueless on how it's possible to advance on that one part, which alone leaves a point to be docked from this zone's score. The map also utilizes branching paths, but it's occasionally unclear on where to go next because of this, leading to some accidental backtracking.
EDIT: After realizing those were spindash platforms that Sonic got stuck on, I've decided to give the map one more point. Just to be sure to make it clear that spindashing elevates the platforms next time. ;)