When a game truly defines a genre, I think it is only appropriate that I give it a try. And so, I wound up buying Carcassonne.
Carcassonne is the tile placing game. In Carcassonne, players take turns drawing and playing a tile. When playing a tile, it must be be placed in a "valid" position (which means that whatever is on the tile matches up with what is on the tiles next to it - no dead-ending roads, castles without walls, etc). After placing the tile, a player has the option of placing a meeple (yes, I believe Carcassonne also brought us meeples - wooden people shaped pieces) on the newly placed tile. Placing meeples is where much of the strategy of the game takes place, as it is what drives the scoring of the game. Meeples can be placed on roads, farms, cloisters, and castles. Whenever one of these things (other than a farm) is "completed" (the castle is completed, the road becomes a circle, etc) then the meeple scores points and becomes available for the user to re-place. Play continues like this until all of the tiles are placed. At this point, farmers score points, and so do all of the meeples on incomplete roads, cloisters and castles. Then, gasp, the player with the most points wins.
What's good and innovative about Carcassonne? Well, we will start with innovative - the whole game is innovative (to me). I had never seen a game where the actual playing of the game is based on placing tiles. Yes, there is a possibility of games before Carcassonne being based on tile placing (feel free to tell me about them in comments), but Carcassonne still managed to define the genre, as it brought it to the gaming market in a big way.
Now that I've told you that it's innovative - is it good? Well, I think that the best aspect of Carcassonne is that it is a nice, simple game. When you want to play a game but don't want to obsess about every move and debate whether it is the best strategy, Carcassonne is your game. It is easy to teach people (though I recommend not beating the snot out of them like what happened to me the first time I played), and can be played by almost anybody - gaming background or not. It is long enough to be engaging, without being so long that you get bored with it (though if you play too many expansions, you might argue that it gets too long).
However, though Carcassonne is very innovative and simple... it didn't click for me. I like to say that I don't care what genre a game belongs to, as long as it does that genre very well. Tile placement may be my exception. I have tried several tile placement games including Carcassonne, Alhambra, Architekton, and a few others. I haven't found any that I think of more highly than "they're ok." Carcassonne falls into this range for me. I can play it, but it's not really one of my preferred games - I would play it when friends want to play it.
Now, for a more objective con, I dislike the reactive nature of Carcassonne. Each turn you must draw a tile, assess the current state of the game, and then place it. There is very little that you can do to form a continuing strategy throughout the game. No matter how well you place things, if you don't draw the correct tiles to allow you to score, there is very little that you can do. I think that this does add to the lightheartedness of the game, and indeed many people will like this. However, this isn't an aspect of games that I am particularly fond of.
Overall, I give Carcassonne a 7.0/10. It is a respectable game that I understand why people enjoy. However, with that said, it appears to have defined a genre that I have discovered that I dislike.
So, admittedly, I'm not a huge fan of tile laying. So, instead of only reading my biased opinion, you might also check out Board Game Family's Carcassonne review, or another Carcassonne review on Games With Two. Or, if you're looking for other gateway games, you might want to check out Tsuro, Cargo Noir, Shadows Over Camelot, or 7 Wonders.