The included adventure clocks in at 64 pages and is a great example of a typical D&D fantasy romp. I approve of it, though it's not without the same occasional writing pitfalls and lack of thorough descriptive examples that some other parts of the adventure module suffer from. It starts out pleasingly linear then quickly opens up for the players to not only spread their roleplaying wings, but find the kind of nonlinearity and sense of openness that tabletop games are known for. The advice throughout slowly scales up the complexity of rules interaction for the new Dungeon Master, at first simply giving you lump experience sums for the players and then later teaching you to do the math yourself.
Sadly, not every part of the adventure follows that same philosophy - once you're into the third chapter the game's clearly done giving you too much advice on how to run your fights and social encounters. Abruptly in the fourth chapter, though, there's thorough descriptions for every encounter again. While some of that could be chalked up to the nature of the third chapter's encounters, it's going to be rather jarring for new Dungeon Masters. The adventure is clearly designed for about four or five players, and with less than four a Dungeon Master is going to have to do a bit of adjusting in the encounters. There are no guidelines for that included - a gross oversight.
Oh, and one thing that's an absolute crime: There's absolutely beautiful maps and illustrations of various points in the adventure, but no way to show them off to the players. A poster map of the region, and maybe the final dungeon, would have been a very wise inclusion. As-is, only the Dungeon Master gets to see them. A real shame - especially since it's easy to get confused about geography.
Okay, starting here are spoilers for the adventure. I'll do another line when they're over
Kicking off with a classic ambush, this is about as archetypal a D&D adventure as you get. While a few plot elements - like the beginning - feel a little generic, the course of the adventure overall is quite nice. There are two strong chapters up front giving players time to learn how their characters act and behave. The third chapter of the adventure is a regional sandbox around the town of Phandalin with a few small dungeons in it, giving players plenty of things to do and helping them learn about self-directing their D&D adventures. A wonderfully crafted web of relationships among the town's inhabitants and the players' motives directs characters towards the adventure seeds scattered around the countryside, and those seeds direct players towards. There's some worry that players will jump the gun and rush towards the adventure's conclusion - and that could realistically happen. DMs who have worry that will come to pass will have to rewrite appropriately - perhaps moving some key clues to new places so that players need to more thoroughly explore before moving on to the final segment. For most, though, the openness will be a boon rather than a burden.
Perhaps the most interesting of the encounters is the ruined town of Thundertree, which has a druid who can help out the players and a dragon living beneath the town's tower. Sadly, the town is the most loosely described of all the mapped areas in the module, with very little guidelines as to how the most key encounter - that with the dragon - should proceed. Other than that the Dragon should run away when reduced to low health. This is emblematic of many fights in the adventure's third chapter, which stand apart from the rest of the adventure because they include only a paragraph at most of combat and roleplaying guidelines for the Dungeon Master.
Pleasingly, there are encounters in the world that have nothing to do with the main plot, like a side adventure involving some orcs and a Red Wizard necromancer. It's lovely worldbuilding and completely admirable as an example for prospective Dungeon Masters learning from this set.
In true D&D style, the last chapter is a large dungeon complex located in old mines. It has a lot of nooks and crannies, with several rooms having no direct bearing on the 'story' of the adventurers in the mine - that's really fun, and gives players some interesting things to discover. The encounters in the mines with a wraith and a hundred year old magical guardian are really interesting and flavorful, and really steal the show in the last chapter. The fight with the Black Spider - the adventure's penultimate mastermind villain - will end up boiling down to a fight to the death on sight for most parties of players. It comes off as vaguely anticlimactic.
Okay, spoilers over.
In the end, this is certainly an above-average way to get introduced to a new game. It's a taste of the new for veterans and a gateway for newbies. However odd choices like the decision to not include better examples of play, better explain how certain adventure encounters should proceed, and the lack of handouts or poster maps hold the Starter Set back. It's not the finest starter set for an RPG ever made, but it's certainly a lot of fun to play and serves as a good taste of things to come. At $20, you're getting your money's worth and then some.
Bottom Line: A strong introduction to the new system and the game, the D&D Starter Set didn't quite blow us away.
Recommendation: If you're a gamer who has always wanted to D&D, this is the time and place to do it.