Pretty much all four of these maps share the same problems, though I'll mostly be focusing on the last two. Ahem:

All four of these maps have the same pointlessly sprawling layout. It's like one large arena but every time you go around a corner it just keeps going. This is pretty bad. Aquamarines is better on this account. It's still a big level, but it's definitely more controlled.

On top of that, they're all pretty much flat. Just one giant box with not enough ammo to shoot at other players.

The texturing and lighting has the same problem. You need to focus more on using just one set, because using multiple texture sets is not helping you and you end up with a lot of weird out-of-place texture choices. Your lighting needs work. There are some nice gradient effects on Sapphires but other areas were entirely done in the same lighting, which is extremely unattractive.

You also have too much extraneous space in the layout; hallways and corridors that just kind of sprawl out away from the main area. This is more prevalent in Zircon and Aquamarine. Your maps are pretty simple in their layout; they all follow the big central arena archetype, which is fine, but any tertiary spaces or hallways need to provide express transit across or around the arena. Pointless sprawl is not good.

Additionally, get rid of the deep water. Again, this is only really a problem in Zircon and Aquamarine, and especially the latter, where you have neck-deep trenches in the middle of the main arena. This is a very bad level design practice and would lead to many many cheap deaths. Incorporating swimming in netmaps rarely pays off.

The best way to improve your mapping style quickly would be to add an element of height into the main arenas to break the sort of monotonous, one-dimensional layout, and to be more conservative with your texture choices but more liberal with your lighting. Get some differential shading in there and it will really liven up these drab and unattractive maps a lot.

It's like, you almost have something here, but you really need to push yourself to get into that sort of "playable" range. Start with making smaller maps. Aquamarine is a decent size, stick with that. Your other three maps are so huge they're unplayable. And I'm glad Aquamarine doesn't have any monsters, because it means I can actually look at the map in peace.

Keep working at it and if you actually follow my advice to some degree you'll have some pretty solid maps before too long.

The two newer maps are great additions, although they are plagued by gamplay-detracting loooong hallways and still quite frugal ammunition placement and overall amount. Still, if I could, I'd score now, more of a 3.25. I think you'd do better with a solo level.

It's not good; it's not bad. Try putting more weapons in; and try being a little more creative on the texturing side of things. All I keep seeing are different shades of rock. Meh.