Welcome Sean, to Tpunk
I haven't quite been to Europe yet but I've been planning and absorbing knowledge for a while. Here is what I gather.
To figure out where you should go you and your fiance should asks yourselves some questions. Do we like art? Do we like to party/go out to nightclubs? Do we like history? Do we like beaches? Do we like outdoorsy activities (ie mountain climbing)? and other similar questions. If you guys say "We love the beach but aren't too in to art and history" Go easy on the museums and spend more of your time at the beach."
Also I recommend going to your public library and checking out videos and DVD on European travel. Many programs such as Rick Steves' Europe and Lonely Planet guides are not only informative in giving you ideas on what to see/do, but are entertaining as well.
Hope I was helpful.
I'm sure more seasoned travellers can offer some more advice.