Background
This is stage 1 of Gradius, the Volcano stage. This stage is the most memorable stage in the series, being (most likely) the first taste of Gradius any fan of the series has gotten. It also contains the memorable song "Challenger 1985", which is the year Gradius came out.
Stage Design
The stage is designed with a rocky mountain landscape in mind, and it does this very well, with some trees added in to make it look more realistic. Near the end of the stage, two mountains appear in the middle of the screen, stuck together. (This is usually a WTF moment for first time players)
Boss/Panic Segment
Volcano
Big Core