The chain reaction concept takes a little while to get your head around but once mastered I find it provides the best modern skirmish games I have ever played. It neatly represents the feeling of a fire fight and the effect of troop quality and leadership very well. The rules provide both the basic game mechanics for infantry, armour and artillery along with army lists (though focussed on mid to late war) and a campaign system. It's a great package based on an excellent series of mechanics that give a great skirmish game.
The use of an interrupted card based initiative system and reducing action dice generates a series of challenges for the player acting at a Company commander level or higher. It works as both a two player and multi-player level and the rules are easy to pick up and play.
The fact that not every unit can act every turn can be a little frustrating at first but it does present a very interesting series of challenges to the player. Obviously for multi-player games it is essential that the distribution of units is properly thought through to avoid prolonged downtime.
The rules are designed around fighting large multi-day actions as units gradually grind to a halt during combat and have to be reorganised overnight. A Divisional Centre of Operations and Forming Up Place are represented and provide reference points for deployment and lines of communication and supply.
The CWG rules sets include background, rules and scenarios as a complete package and the original two volumes were The Canadians in Europe and Dropzone which dealt with major airbourne campaigns (Crete and Market Garden). A third early war volume (Invasion '40) has also been released and is available, along with a .pdf version of the rules as part of the CWP offering at Saber's Edge Hobbies & Games (whose website appears to be down at the moment).
The obvious omission from this list is a set of rules at Regimental level. I have used Spearhead for this but, whilst a decent set of rules, I'm afraid they don't float my boat.