COH is a fantastic game, but i would highly recommend 2gb of RAM, not only does it speed up general game play and loading times but it allows you to put a load of the options up as well.
Back to the game, the majority of the combat takes the form of controlling squads of men, this is typically 6 men that move together, but they adapt to their surroundings. All the environment is destructable and provides some form of cover for infantry.
Tanks are to me a "luxury" if you could put it that way. Put it like this, if you see a tank alarm bells start ringing because you most likely need to get something that can actually kill the tank to the location, be it an AT gun or a squad of riflemen with stickybombs.
The historical accuracy is impressive and adds to the immersion, as well as the best voiceovers and sound effects in any game.
Its one of those classic games which is easy to get the grip off, but hard to master and this makes it great. Also, there isnt too much in the way of buildings so its not like AOE or Rise of Nations where your constantly building houses etc. However you do get to build ample fortifications such as barbed wire, tank traps and sandbags.
The idea is to capture and hold different regions of the map, each of which contain a flag which will provide a certain amount of manpower, munitions or fuel per minute. You also get command points which are very similar to those in LOTR battle for middle earth.
So basically, it mixes a good setting with lots of tried and tested RTS elements from other games really well to make it fun, tactical and good online.