In the first 4e game I DM'd, we ran just 3 PCs (Dwarven fighter, Dragonborn Paladin and Halfling rogue). All of us had over 20 years of experience with previous D&D editions, Warhammer, GURPS, and others.
As a DM, I found it very easy to scale the adventure, and make changes on the fly to make the game really interesting. From the player's perspective, they found that the game was more strategic, which made it very interesting. The players quickly learned how to work together to set up for combat and possible combat situations. They also had chances to roleplay quiet a lot, and the skill challenges made the game more cinematic, not just combat only scenarios.
In 3 1/2 hours, we were able to complete 2 smaller combat enounters, 2 larger combat encounters, and 2 skill challenges and other roleplaying opportunities. I was able to cut out parts of the dungeon to allow the characters to finish the quest. In addition, rounds went quickly, and it did play more like our favorite movies.