It's one of my least favorite airports in Europe. The number of times my luggage got lost there alone is enough for me to avoid whenever possible. The shops and restaurants are also extremely bland.
Changing between terminals at Heathrow is much less fun.
CDG I find confusing.
I decided to stay at a Heathrow airport hotel a while back. Turned out I had to change terminals and I'm pretty sure it took me at least as long as getting a shuttle bus to one of the hotels would have taken.
You often have to walk quite a ways too.
Overall though Heathrow is pretty good among the large European airports.
Worse than Frankfurt? It seems like the only food you can get there is a hot-dog...