Yep, what Phil says.
I use Neil Thomas's rules or at least my slightly modified version of them for most of the games I run, Ancient - battles against Rome, Medieval - Bruce's Campaign in NE Scotland (which ended up on film

!), 18thC - Bier wars Imaginations, 19thC - Napoleonics and a couple of Garibaldi vs Naples games.
The basic mechanisms work, are simple to learn, simple to play, get a good result, don't need days to play and cope with most things the average gamer can chuck at them. That ticks the boxes I need. The changes I've made have been to add my own flavour and viewpoint, nothing heavy - the obvious one being moving to single bases and using dice to record hits.
Give them a go!