Being an old "tanker" out of M4A2E8 Shermans from the 60's, I've always had a fondness for tank simulations. I picked up one called Steal Beasts that I've found to be simply awesome. I think it's a real "sleeper" and probably the best modern tank simulation I've encountered.
I have spent a lot of money over the years on various flight, tank and general war gaming simulations, but none of them have ever retained my interest as much as Steel Beasts. This is a first class simulation dedicated to the serious realism buff and I've thoroughly enjoyed the depth of immersion, terrific A/I and overall sense of strategic real world complexity that the programming team have been able to build into this product. It has a complete multi-player option and I've really enjoyed the on-line sessions with a dozen or so guys.
There's one issue you'll have to get your head around before making a judgment call on this product. The authors began writing this sim in 1996 before the advent of 3d cards, so it runs in 640x480 and a common complaint for newbies is the graphics seem primitive by today's 3d hardware standards. I had trouble at first with this, but once I spent about a week truly learning how masterful the actual simulation is, I began to overlook the older style graphics. The bonus is that it runs on my Sony Laptop without a CDROM for use when I travel on the road and only needs to use the CDROM for upgrades.
Give it a try. If you're into tanks, I highly recommend this one. They have a downloadable demo and the primary site for eSim Games is:
http://www.esimgames.com/
