Too much of everything. Try doing more with less. Tiles themselves aren't sooo bad. Dense and overlapping objects make mine eyes bleed.

For instance, many, many of those enemies are both redundant and unsightly. Six missiles or gauss cannons in roughly the same area do nothing that one or maybe two couldn't do. Let's say the flood of drones is integral to your virus idea. Show some restraint in loading orher areas with superfluous enemies, as in the upper left.
Is this map fun, in your opinion? The action looks very random and unstrategable. I think with some refinement this could become playable at least.