C-Bills and MC can both be used to purchase new 'Mechs, but only C-Bills can be used to purchase weapons, armor, and other equipment. Only MC can buy Premium time, which confers an experience boost, and aesthetic adornments for your 'Mech like new paint and patterns. These MC-only items do not confer any in-game advantage (though painting your 'Mech bright red with yellow stripes may confer a disadvantage). MC is also used to buy premium Hero 'Mechs. Hero 'Mechs are flashy and carry different equipment, but are not necessarily better than the non-premium 'Mechs.
Progression can be slow without investing money in the game. Four trial 'Mechs are always available to play, and change often, so you can usually try out a 'Mech before you commit. New players get a Cadet bonus, a boost to C-Bills and experience earned for 25 matches, which should be enough to purchase your first 'Mech, but after that it can be long haul to save up for a new chassis. If you buy MC, you can stretch out your Cadet bonus by supplementing it with Premium time, a temporary boost to your C-Bill and experience point earnings.
Once you have a 'Mech you like, it's an incredibly easy game to pick up and play. With matches ending so quickly, you can easily squeeze six rounds into an hour of gameplay. You lose little momentum between matches, quickly forgetting devastating losses as you queue into a new match. Even when piloting a heavy or assault class 'Mech, which run barely one-third the speed of light 'Mechs, each match has a sense of urgency that means trudging across a lava field never feels like a death march.
One major feature I'm still waiting for is Community Warfare, which will introduce the BattleTech story of the Clan Invasion and allow players to join Clans to fight over galactic territory. More information on Community Warfare and other upgrades to the game are expected September 26, when Infinite Game Publishing and Piranha Games will host an official launch event.
MechWarrior Online captures the feel and customizability of the old MechWarrior games. The shudder as your 'Mech comes online, shakily loads your HUD and announces that its weapon systems are operational makes you feel like you're really piloting a mechanical war machine powered by a nuclear reactor and taller than your house. The different 'Mech weight classes create a battlefield with distinct roles, advantages, and disadvantages. The depth of customization and the fast gameplay has kept me coming back to this game since last December, and I look forward to playing it for months more.