If you have played 'To the Strongest', you will quickly pick up these rules as they use many of the same mechanisms. The key features are the use of a grid, obviating the need for measurements. They also use playing cards instead of dice.
The main changes are to the shooting and melee rules, which are a bit more complex, to reflect the importance of firepower and the different tactical approaches to melee.
You can use any scale and even within scales there are a range of options which allow players to use existing armies and basing - always a plus. There is a points system and a couple of army lists, with more to come. These could easily be tweaked for other renaissance armies, and no doubt will be once the forum is going strong. You can also play quite small games, up to multi-player games.
Some folk don't like the use of playing cards on aesthetic grounds. I have a couple of small packs that came from posh xmas crackers, but you can use chits if it really bothers you. Some heretics are apparently even using D10s!
The grid is another criticism. I have a lovely Deep Cut mouse mat with 100mm squares, which as you can see from the photos, barely shows. As an alternative you can just put dots on the corners. The real advantage of the grid system is the speed of play and the absence of measurement squabbles. Mine also doubles up as a mat for the Rommel WW2 rules.
My test game used 100 point Royalist and Parliamentary armies of the mid-war period in 15mm. I am not a regular TtheS player, but I quickly picked up the mechanisms again. The one irritating omission is a quick reference sheet. Flicking backwards and forwards on my iPad is not ideal and it meant I kept missing some of the factors, particularly in the activation phase.
Other than that, the game flowed well and felt like an ECW game. I will stick to Pikeman's Lament for skirmish games and Pike & Shotte for the big battles in 28mm. However, this is a good in-between game for my 15mm figures that can easily be finished in an evening.
Some photos from my game, starting with the set up.
First turn with the cards showing.
The dreaded ace, that brings that brigade to a grinding halt.
The Royalists are powering through on the left flank and making good progress on the right as well. The question is, can they be rallied before pursuing away. Nice rule system for this.
Finally, a breakthrough in the centre and so King Charles lives to fight another day. The dice are ammo markers. I am not convinced this level of complexity is required, but it works well for horse melee.