Here are a few of my thoughts, chicmunk:
The texturing in this room is okay, I'm just kinda weirded out by the walls. What is that texture, and what does it mean? The floor and ceiling make sense, and the lava and crystals look pretty good, I just wonder what this area is supposed to BE, ya know? It doesn't feel like a cave because those walls are confusing.
NOTE: INCOMING DISSUSSION ON SECTOR LIGHTING! Please read if you're still newish to mapping and wanna make your levels feel more natural!
This area could look a lot better if you put some attention into lighting. Every room must have a light source. In this room, it's the lava. Lava should be super bright, and bright light sources are "harsh" (they cast well-defined shadows). You can represent this harshness if you darkened every sector that doesn't have lava! Just lower the lighting of the those sectors by a good (noticeable-and-then-some) amount and I think the room will a ton better.
Actually, looking at the rest of the screenshots, it's clear that you've disregarded lighting for the majority of the map except for the part where you platform across those colored pillars. "Outside" lighting should never be 255! This brightness level makes everything look kinda flat and can actually screw with your depth perception. Light level 240 generally makes things easier on the eyes and helps with judging distances. Just remember that outsides should be bright, insides should be darker, and light should only come from light sources (the sky, torches, lava, etc). If you have a large amount of underground areas, then place more torches, lava, or cracks in the ceiling. Then decrease the light level of sectors as they move away from those sources (though don't make it 134 or below unless you want it pitch-black). It makes the level feel more sensible and looks better too!
Lack of sensible lighting can give your levels an "off" feeling. It's a feeling of artificiality that your brain notices, even if you don't really notice it happening. This map totally has that feeling, and a lot of it is the lighting.
The rest of this feeling comes from the train-of-thought level design. A lot of SUGOI 1 maps suffered from this feeling, but that's okay since beginner-ish maps tend to feel artificial as a rule lol. It takes tons of practice to rid this feeling from your levels and get them looking like places that could loosely "exist".
Oh, and your giant room with "SUGOI 2" looks silly :P