My eighteen-year-old self is appalled that I liked Wells more than Karpov's two magisterial tomes, but it just shows that I'm not really serious about chess any more. I want a Black defence to 1. e4 that I can use when I play the occasional speed game on ICC, and I'm not planning to spend most of my waking hours for the next month perfecting my understanding of the analysis. Once, perhaps, but now I have neither the time nor the motivation. Though I must say that I'm incredibly impressed by Karpov's books. He played four matches (Spassky, Sokolov, Kamsky and Timman) where the Caro-Kann was his main defence, and he and his team must have put in hundreds or even thousands of hours of work preparing it. We're getting the benefit of all that preparation in his books, and I'm just sorry I'm not in a position to appreciate it more.
Wells is no Karpov, but he's a Grandmaster-level player who has played the Caro-Kann a fair amount, and he does a fine job of summarising the key lines inside less than 200 pages. If you're a casual player who's trying to find an opening that helps you get a bit better, you might want to consider buying it. The nice thing about the Caro-Kann is that it's very solid, and, if you're not playing at top international level, you don't really need to learn a ton of theory; contrast that with the Sicilian, where even at club level they'll kill you dead if you aren't up on at least the first dozen moves. White starts 1. e4, and you respond ... c6.
Now, pretty much whatever White does, you've set yourself up to play ... d5 next. Usually, White plays 2. d4, and so we get this position:
You have a foothold in the center and no weaknesses. The downside is that you're going to find it a little difficult getting your pieces out - in particular, the c6 pawn is occupying the square your Queen's Knight would like to have - but you'll have time to sort that out if you're careful. You're aiming for a slow, manoeuvering game, where you'll first untangle and then counterattack if possible.
Of course, even in the Caro-Kann there are ways for White to try and attack. The most dangerous one is the Advance variation: White moves forward with 3. e5, gaining space.
Black usually now puts his bishop on f5, but White can try and chase it with a timely g4, and things get complicated; Karpov devotes most of a book to analysing the resulting mess. Luckily, though, my experience is that people below strong amateur level rarely play the Advance.