Baldur's Gate: Dark Alliance...with guns.
FO: BOS is a top-down, hack-n-slash action RPG in a post-nuclear setting. Your character is an initiate in a post-apocalyptic version of an order of knights, the Brotherhood of Steel. Your goal is to track down the rest of the Brotherhood, while restoring a semblance of order to human civilizations along the way.
The Good:
The RPG elements. I enjoy RPG's, particulary action RPG's, but I get a little tired of the fantasy setting of 95% of RPG's. BOS brings games like Baldur's Gate and Diablo to a post-nuclear, urban, fictional yet somewhat realistic setting. And it does it fairly succesfully. The variety of weapons and armor is good, and you can find a lot of things while scavenging. You can't save at will, but there is no shortage of save points, which are in the form of kiosks.
The dialogue with other characters is also good, unfortunately there's not enough of it. The music and sounds are also pretty good.
If you enjoy the gameplay and want more, there is some replayability here. When you beat the game, you gain access to a few extra characters to play as. Or you can use your character from the last game. You get to keep your levels and character upgrades, but unfortunately you lose all weapons, armor, and other items. This is good if you plan to play on the "wastelander" difficulty, which is punishingly difficult and only available after you beat the "hard" level. This is great for hardcore RPG gamers who just want to level the character and max out all stats, although it involves a lot of grinding and isn't worth it unless you really love the game.
The Bad:
The game is very linear. There are a few side quests which will get you extra experience points, but other than that you're basically following a line. When you talk to NPC's, you can choose from different lines of dialogue, but the end result is always the same. Basically, if you play this game for an hour, you should keep playing it if you're enjoying yourself, or quit if you're not, because the gameplay really doesn't change at all.
Also, this game is not a direct sequel, and it's not canon to the Fallout universe. If you're a huge Fallout fan and you think this is Fallout 2.5, you're wrong.
My opinion:
FO: BOS is a decent game, especially if you like the genre. Fallout 3 (an awesome game) is often described as Oblivion with guns, and that's not an insult since Oblivion is an amazing game. So why do people compare BOS with Baldur's Gate: Dark Alliance with disgust? Dark Alliance is a good game, BOS is just like it, but with guns. A lot of the harsh criticism comes from faithful Fallout fans who consider this an insult to the Fallout name. But if you take this game for what it is, an action RPG that's not part of the Fallout series (despite having the name), it's an enjoyable game.
If I didn't have a huge backlog of games I want to play, I would have probably given this another playthrough.