I have used the Lonely Planet guides in Asia, the Middle East, and in Europe. Lately, they seem to have lost their way. Originally, the LP guides were for people who had travelled at least a little bit before and needed some pointers to an area. The guides usually had some sort of walking tours in the cities they indicated. Their guides have become filled with useless colour photos of generic scenes, The quirky, fresh information has largely disappeared -- In the summer of 2004, I used the LP guides for both Portugal and Spain. I travelled for about three months. I had been in both places before and had used a LP guide. The most recent guides are stale and minimally updated. They are also occassionally misleading; especially concerning food. Sadly, the LP guide to Spain is not worth the weight that goes along with carrying it.
A telling thing is that I saw several tourists with back packs hanging on both their back and front clutching their LP guides while staggering and sight-seeing through Spanish cities in the afternoon. This is telling for two reasons: (one) In the afternoon, in Spain, there is little to do other than siesta, eat, or drink; it is not the time to sight-see (two) Carrying two packs is carrying one pack too many; the prior generation of LP users were experienced travellers (not tourists) and would find two packs foolish. Anyhow, somehow, LP has lost focus and now better serves the Lets Go crowd instead of more experienced travellers.
My advice: If this is your first trip to Europe, consider buying Lets Go. If you already know how to get your bags off of the airplane, search for an alternative by looking at country specific guides; do not buy a LP guide just because you had happily used one before.