A variety of sanctioned tournament types are provided by Wizards of the Coast for the Magic: The Gathering CCG. In general, the constructed style (where players bring their own deck, meeting assorted guidelines as to which sets are permitted) is easiest to administer and so play level ranges from Friday Night Magic (low key evening events at local stores) right up to the invitation only Pro Tour circuit. The alternative to constructed is limited- where each player is supplied with an initial small card pool and has less than an hour to try and forge an optimal deck from it. This should make limited far more accessible to new or more casual players- rather than having to determine and finance a highly tuned constructed deck, you get to level the field with all players at a similar resource level.
Of the two limited approaches, this is even more true of sealed deck, which omits the complexities and time requirements of a booster or rochester draft. In some ways, all new players are effectively playing sealed- they purchase a few packs, and slowly trade for cards to enhance their pet deck. Indeed, this was the way that Richard Garfield invisaged the game- with powerful cards balanced by their scarcity in the environment, rather than being obtained in playsets of four through internet mail order. Sealed deck limited could offer the best chance to recreate this environment, with competition being kept somewhat in check. Sadly, most sealed deck tournaments only arise as part of the pro tour qualifier season: where competition will be particularly cutthroat. So for a friendly, moderately competitive event for all, where can you turn? The prerelease.
A pre-release tournament is sealed deck with a twist- the cards being used are so new, they aren't even for sale yet (with the official launch being a couple of weeks after the prerelease). This means that people can only know the cards through online spoilers, where they exist- and that is little substitute for experience or simply having them in front of you to get an appreciation of what works and what doesn't. The focus then isn't so much on winning- although a display of 36 boosters awaits the winner- as on discovery of new cards and combos. Rarely do you here people talking about the top players: rather, the discussion is of whatever unbelievable cards you opened, or outrageous combos have been uncovered. With the test of time, those cards might turn out to be somewhat less than awesome than expected; or a sleeper hit may emerge that only you had the foresight to play at the prerelease. But on the day, that doesn't matter: it's all about fun!
As an additional incentive (beyond the cards you receive for the tournament, which are yours to keep), special edition prerelease cards are provided, but only for those who play in the event. This enforced scarcity can increase their value amongst certain collectors, although often a big, splashy marquee card rather than a tournament powerhouse is chosen so sentimental value may outweigh the cash amount. Speaking of collectors, the combination of a new set and different players can lead to some great trading opportunities, whether you want to shift old cards to a more receptive market or fancy taking a gamble on which of the new cards will turn out to be bombs.
Prereleases tend to be at a one-per-city level, occur worldwide, and are run by the same TOs that manage PTQs and other formal local events. Some organisers will run back-to-back tournaments on Saturday and Sunday; the maddest will have them kicking off every 12 hours or so for the entire weekend, if midnight gaming is your thing. Smaller stores can run a sneak preview tournament, functionally identical to a prerelease except without the prerelease card (unless some have been appropriated from an undersubscribed prerelease), and with a smaller prize pool. These take place the weekend after the prerelease itself.
Prereleases tend to wrap up a bit faster than a usual sealed deck PTQ: firstly, deck registration and subsequent exchange isn't usually bothered with (it's hard to smuggle in cards from a set that isn't on sale, and the stakes aren't all that high to warrant the effort); plus some organisers stop after the swiss rounds without a Top 8 draft- check with them first if you're not sure.
So if you've only played magic casually, haven't played for years, or have become disillusioned with the arms race nature of constructed, why not indulge your inner Timmy, Power Gamer and give a prerelease a shot?