As a long time fan of Columbia's games, here are my few cents on the topic. The games run from simple (Quebec 1759) which can be completed in an hour or two, to incredibly detailed and complex EuroFront). EuroFront is the game which links all the other [x]Front games into one mammoth game involving multiple players, diplomacy, alliances, etc etc...

My absolute favourite two block games are Rommel in the Desert and EastFront. Rommel in the Desert has an elegant system of supply which allows you to move, fight, and do other things. It's fairly fast paced and once you get used to the setup and mechanics, you should be able to finish the game easily in an evening.

EastFront is in a word brilliant. It has an elegant "supply" supply system by using "steps" on headquarter units in order to command your other units and give them support during combat. It uses scenarios or you can link all the scenarios together to do a complete campaign. In my experience, a scenario takes around 4-6 hours to play - your mileage may vary. Columbia also sells a computer version of EastFront which lets you play opponents via email or direct connection.

The nice thing about the block games is it gives you an easy "fog of war" (who knows where your opponent has set up what!). Overall, I feel their games are excellent value for the money.