That map definitely deserves to be finished. I don't know if a whole extra area would help, because the map feels too sprawly for the amount you've got in each space.
My comments:
- Most of the trouble I see with the layout is distance, specifically between the RG/MH area and the central drum. There's a long boring walk from one to the other no matter what direction you go. I say do whatever you can to chop that space and bring those two closer together if not integrate them entirely into something more open. That'll make both spaces more interesting (because right now they're pretty simple) and speed up movement around the map.
- The RG room has two ways in that each lead to one other way out each, so all you ever do is run through it without navigating. Some interconnection in here between the spaces is needed. Merging it with the center room would go a long way, and/or you could also do this:
http://www.lunaran.com/pics/stormtrigger6.jpg
- I really like how the center room and the outer yard are one big space if you peek up over the top. The outer area feels like it needs more variety in the walkable space for its size, though. There's one unintentional little loop around the slime waterfall that would be neat if it were detailed a bit and made visually intentional, with some stray bonuses.
http://www.lunaran.com/pics/stormtrigger1.jpg
Little additions like this elsewhere would help add complexity to big and otherwise kind of straightforward areas.
- A ledge or two more cut into the rocks behind the lampposts would be nice also, because they could be used as cover rather than decoration.
http://www.lunaran.com/pics/stormtrigger2.jpg
- There's two areas above to either side of the big drum that would be nice to see turned into play space also. The one on one side could provide a hole over the MH to drop through if you brought that area in, and the other (that kind of narrow space alongside/on top of the megapipe) could lead back into the central room, and provide a nice tight/interesting place for combat.
http://www.lunaran.com/pics/stormtrigger3.jpg
http://www.lunaran.com/pics/stormtrigger5.jpg
I say this because everything else in the map is a pretty standard open width, and having more hidden away places like this or behind the lampposts would add a lot of variety to the space. Adding more such variety in the inner spaces would be even better, so the whole map isn't made for railgun whores.
- There's an easy jump to the RA platform on one end but not the other. Putting a second ramp here and making you jump to the RA from either end would make it more dangerous to grab. (Even separating it into three platforms to make you have to jump twice to get to it.)
http://www.lunaran.com/pics/stormtrigger4.jpg
Having the RA available immediately after grabbing the RL might be unbalancing, too, but a lot about the item placement might have to change.
- If there's no way out of the slime, kill me instantly when I fall in. :)