A few changes to close combat (specifically charges) that i like to use to spice things up.
Close Combat<?
When a unit is charged it can respond in many ways. For every charged unit roll 2d6, and compare below.
3-5 Retreat! The unit crumbles under the pressure of the approaching horde and falls back. Roll 1d6 to see the distance that the unit retreats (jump infantry of all kinds roll 2d6). This can often be small enough that it will not matter, and result in combat anyway. Under such circumstances the unit must halve (rounding down) the number of attacks it makes as it struggles to prepare itself for the onslaught.
6-9 Stand firm! The unit Holds its ground, and combat begins as normal.
10-12 Counter Attack! Perhaps through bravery, or stupidity the defending troops launch a counter attack of their own. Each unit moves half way towards the other, meeting in the middle.
Both units count as charging, gaining the normal benefits.
Modifiers
Leadership is an important factor in such decisions. For every point over 8, add 1 to the dice roll. For every point under, minus 1 to the dice roll. Note special rules and war gear that artificially increase a squads leadership by adopting another squads (Imperial command squads, synapse creatures) do not count for this as combat happens in such a rush as units rely on instinct.
If the unit being charged is outnumbered 2:1 they suffer -1, 3:1 they suffer -2 and so on.
Units which are fearless gain +2 to the result.
Eg: A unit of Vespid being charged by Space marines roll 2d6 and get a result of 9, as the strain leader has a leadership of 9, +1 is added to this score giving a total of 10. The vespid are however outnumbered 2:1 (10 marines to 5 vespid) resulting in -1 for a total of 9. The vespids now stand their ground and combat begins as normal.