Simple bot AI, (zombie-tracking) with abstracted 'flight controls'; this is just a struct. in CUserInput.h - I like it, because I can use it to represent true user-input aswell as playback-type stuff and computer-generated input.

Particle system - used in a true dynamic way and also in an optimized-type way for the projectile 'lasers'.

Patch-based fixed-LOD terrain algo; this is definitely suboptimal -- inefficient use of vertex buffers causes excessive state switching and poor performance, but it's interesting to note that even a suboptimal design can be sufficient in certain cases. Quadtree frustrum culling is applied here, nothing too fancy. It's possibly slightly unusual in that I supply colour data in addition to dynamic D3D lighting.

Oh yeah, variable # of D3D lights are supported, and are dynamically turned on/off in response to gameitem proximity. Leads to some pretty shading under certain circumstances, but also to a strange blinking effect!

A 'screen-overlay' system; an attempt at a better way of drawing stuff like HUDs -- all these vertices come from the same vertex buffer.

Useful class: CCmdLineParser -- I'll definitely be reusing this one!

Groovy (read: quite fast) terrain-ship collision detection, see CTerrain::LERPdY().

Billboards, scene output to BMP, mouse smoothing, basic flight-physics modelling (actually a complete hack, to call it a model would be silly) with a strange 'never-done-before' flight-sim meets Quake-type strafe function :@

Menu handling code, and re-entrant game code, to support level movement and game over type scenarios (not to be underestimated, proved quite tricky).