Well - as far as Matterhorn, FL side is longer, slower, and less rough. TL side is shorter, faster and more of a coaster like ride. Rode them both last week, and both were quite fun! I noticed the difference, but don't think someone who didn't know would necessarily notice.
Haunted Mansion has some neat differences. The entire building is completely different on the outside, there is less walking at DL before you get to the buggies, and the outside queue is different.
Pirates is quite a bit different as well. The queue is not as elaborate at DL, but you'll be able to get a glimpse of the Blue Bayou Restaurant as you board and float to the beginning tof the ride. The ride itself, I think, is better at DL. There are 2 fun waterfalls (much larger than at WDW), and I think there is more to the acutual ride.
Buzz Lightyear is also a bit different. The inside queue is shorter, and the ride itself, although very similar, has some differences. The targets look different, and you get more points for shooting triangles than circles and squares. The guns are attatched to the vehicles by cords, so you are able to aim better without have to constantly turn your car around in circles. It was a lot of fun. It is also in Tomorrow Land, not FL.
The dark rides in FL are a bit different. The nursery scene in Peter Pan is larger and more detailed, Mr Toad is still around, and the Dumbo ride is beautifully placed over a water fountain. The tea cups are uncovered, and have great Japanese lanterns hanging over them.
Thunder Mountain seems the same to me, as does Splash Mountain. If Space Mountain is open when you get there, it's smaller and the coasters take sharper turns - also, there is only 1 track (I think!).
Be prepared for a much smaller castle! We were even surprised after visiting WDW for the first time just how little the DL castle looked! But it is beautiful and charming!
Not-To-Be-Missed (IMHO) for a DL Newbie Who's A WDW Vet
DL's Fantasmic
Indinana Jones
Alice in Wonderland Ride
Casey Jr
Storybook Canal Boats
Riverboat Columbia
Eat at the Blue Bayou
At Ca Adv:
Soarin' Over CA
Grizzly River Run (AK Kali River Rapids)
TOT (I hear there are some neat differences)
Sun Wheel
California Screamin' (nothing like Rockin' Roller Coaster)
Electrical Parade
Redwood Creek Challenge Trail
Obviously these are just the ones to see the differences of the park - for someone who's never gone to WDW, the list would be different
Have Fun!