It's definitely a really different sort of format. Besides the commander, the most important aspects is that it's one of each card (as opposed to the normal 4 copies), and it's multiplayer.
Having one of each card and being based around a "commander" lends itself well to certain cards.
Cards that clone creatures (capable of copying opposing commanders, removing them from play), various unique mana sources (if you're playing red/green, you could go with something like one Stomping Grounds, one Gruul Guildgate, one Rootbound Crag, etc), cards that support your commander (equips and enchantments that protect your commander).
There are alot of cards that are definitely intended for the format, with some absolutely vital. Command Tower (land that gives you mana in your commander's colors) is a big one. You can shoot pretty big in terms of high mana spells because commander is a pretty slow format (Aw man, we all built up these huge armies, one guy wipes the field, game takes 6 hours).
It's multiplayer, so, take that into account. A card like Insurrection(take control of all creatures for one turn) is kinda worthless in regular one v one magic, but it has alot more value in commander (more players, more creatures).
