As far as campaign systems go, there needs to be a split. There will always be the Holy Grail of the large multi-player campaign, played by many nations. However, at the bottom end of the scale, a nice simple 'linear' type campaign system that can be played by two players is also required.

Then, dare I say it, a mid level system, both regular and linear.

Large Campaign Systems - we all know what these are and what should be in them. Tony Bath's book is a good starting point there.

Linear Campaigns - there are two ways of looking at linear campaigns. One is across time and the other is across geography.

Time Linear - take somewhere like Spain, where over a period of a thousand years the Iberian Peninsular was invaded and/or settled and/or controlled by Celts, Carthaginians, Romans, Vandals, Visigoths, Moors, Christian kingdoms and so on. Then there was Britain, with the Picts, Celts, Romans, Saxons, Vikings, Normans.

A time linear campaign is a method of moving along the time lines with various protagonists in control (and still in existence) depending on the performance of their forebears. Harder to do with a rule set that requires lots of figures but possible by morphing armies.

Geographical Linear - at it simplest level, take two states, say Rome and Carthage. Draw a long thin map with Carthage at one end and Rome at the other. Mark the map off into, say, 5 tables, with Table 1 in Carthage and Table 5 Rome. Both sides start with a roughly even force and commence battling on Table 3. If the Romans win on three, then the next battle occurs on table 2. The Carthaginians get back a percentage of their lost troops plus a top up of lower quality troops from Carthage. The Romans get back a higher percentage of lost troops and fewer troops from home (is further away now). Some of their poorer quality troops will get better in quality. They fight again. If Carthage loses, next battle is on table one. If Rome loses, next battle is on table 3 again (the terrain can be randomized a bit so it is not too much like fighting the same bit of dirt again). Replacements occur as before.

Keep repeating this until an army has lost on its home table. A nice little two person campaign system, simple to run and not requiring umpires or such. Perfect for almost all us wargames who have at least one regular opponent available that we play with from time to time.