As a mapper, Slave is really taking some considerable strides in technical ability, but has some problems with diversity; in short, many of his maps feel similar to each other and few of them are especially compelling on their own. When put in a pack together, the sameness of many of these maps becomes a big problem in choosing a map to play.
I find that stylistically the same sets of architectural elements find themselves present in almost all of his maps, which isn't necessarily bad (I am guilty of the same thing) but when they are as prevalent as they are in some maps here, they become less of a convincing motif and more closely resemble a lack of creativity. I think Ascent, Concentration Moon, and Firefly are basically the same map, for example; different texture sets, sure, but the weapon choices and general flow are very similar (and I still think Ascent is the best). Rainfall, In Limbo, and Deep Blue Day are also remarkably similar, or at least to me.
I think the problem is that most maps here are less a collection of rooms and more a collection of corridors and passageways. In my experience, rooms are both more fun to play in and more compelling as a composition. In that sense, Leek Hills, Riki Tiki Tavi, Ascent, and Tiger Mountain are some of the best maps in the pack. Tiger Mountain and Leek Hills especially provide a great balance between big, interesting main spaces, and functional secondary corridors and spaces that make the maps especially successful, whereas maps like Endless Night and Airbag are less memorable or interesting.
Other maps have problems with height changes that are both too dramatic and too drastic to really work well for this game. There's nothing specifically wrong with big heights and a dynamic use of them, but it can reach the point where the flow is so stilted, and too focused on going up and down, that it interrupts the gameplay. Airbag, Cloud of Eiderdown, and Ocean of Noise all have this problem to a severe extent. Maps that use height changes well are Rainfall and Deep Blue Day; in these cases, higher and lower elevations still interact well both by themselves and with each other, and the focus of flow is still more horizontal than vertical.
I think a constructive mapping exercise for Slave is to make a few maps that are simpler and focus on big issues rather than small ones. Cosmic Clouds still lacks a traditional arena, which is okay, but I believe that making an arena is an easy, fun, and productive exercise; successful arenas put all of the player focus on straightforward combat, which is something that is lost in the shuffle to some extent currently in this pack. Good arena maps are enjoyable and memorable. Making more maps that focus on one or two main rooms, with less focus on corridors, side spaces, ledges, and so on, would also probably be constructive. Riki Tiki Tavi is one such map, and one of the most flexible and most fun. Over Fire Island is a case where a good main space is tarnished by having too much cruft in the upper levels, which are so high they're detached from the main flow.
To me, the best maps are Ascent, Leek Hills, Tiger Mountain, and Riki Tiki Tavi. That is not, however, an invitation to make more maps like them. It would be better to take some of the metaphorical ideas that make them successful -- big spaces, smooth flow, memorable design -- and employ them in new maps.
And make less water maps. Take a look at the screenshots posted here -- five of them look like they could be the same map. I would like to see more maps that used Jjaro and Lava, especially. Different texture sets would encourage different architectural quirks and styles, which I think would be a good exercise.
I would like to give this pack a 4.5 -- it really is almost there, but it falls only a little short of being excellent material.