Choosing gear is a key to surviving deeper dungeons. Rather than level your character, your gear earns experience every time you complete a floor. Each level brings new abilities and power upgrades, forcing you to really think about what you're wearing. It's not enough to just grab the most powerful items on the rack. Instead, you need to decide what abilities are important and what armor you're willing to give up in order to earn new upgrades.
Combat is incredibly easy; just point and click. However, just hacking away won't get you anywhere since you need to learn attack patterns and rely on party tactics if you want to defeat larger bosses or enemy swarms. Spiral Knights offers a couple of control options. It's possible to just play with your mouse, though a WASD and mouse variation is available. Both options are good, though I preferred plugging in a controller.
Spiral Knights is a "Free to Play" game. Every day players are given one hundred units of Mist Energy, which is used to enter dungeons or create new items. One hundred units is usually enough to get a decent amount of play, though players can also use real money to purchase more energy. Additionally, players can buy access to special upgrades. Although there's usually a stigma associated with this sort of "velvet rope" approach, it's not a bad deal. The special items are enough to give players a decent boost, though not to the point where non-payers won't have fun.
Time will tell just how successful Spiral Knights will become, but based on my time with it, there's plenty of reason to be optimistic. It's a fun adventure, especially for fans of dungeon hacks and Zelda. Best of all, it is free, so give it a try and have fun.