I have never stayed onsite because of the price (although I hope to this upcoming summer). There are TONS of offsite hotels that are within about the same walking distance as the Paradise Pier and the DL hotels. My guess is that since you stay onsite at WDW, you will not want to stay at a cheap motel at DL, however the price differences are huge for not many benefits. Just something to think about.
For good table service restaurants, check out the Blue Bayou in DL. It is THE restaurant to go to at DL. You are sitting next to a bayou with the Pirates ride floating next to you. Very nice and very good food, but you need to make reservations fast.
Also, one major aspect that is different between WDW and DL is that everything is within walking distance. It takes less than a minute to park hop. Downtown Disney is a minute away from the park entrances and the onsite hotels are just past DTD. This makes dining in DL's DTD much easier than at WDW because you can just hop out of the park and walk 5 minutes to any restaurant. Or you can take the monorail from Tomorrowland to right next to the Rainforest Cafe and vice versa.
Here are some rides unique to DLR that you won't want to miss:
Indiana Jones (ride vehicles like Dinosaur, much better themed with an amazing que line)
Pirate's Lair (Tom Sawyer Island with a pirate theme, lots of pirate caves to explore, a pirate show, CMs dressed up as pirates just wandering the island, plus a Captain Jack Sparrow meet & greet)
Pinocchio (Fantasyland dark ride *a little scary)
Alice in Wonderland (Fantasyland dark ride)
Mr. Toad's Wild Ride (Fantasyland dark ride *a little scary)
Roger Rabbit's Cartoon Spin (Spinning Toontown dark ride)
Matterhorn (1st ever tubular steel coaster)
Casey Jr. Circus Train and Storybookland Canal Boats (gentle rides through Storybookland. Good for kids)
Everything at DCA except Soarin, ToT, Muppets and Bug movies, and Turtle Talk
Rides that are significantly different:
Jungle Cruise (different jokes, some different scenes)
PotC (much longer and better)
Pooh (no long lines at DL because it's tucked away in the corner, different ride vehicle)
Splash (different seating, shorter ride, not as long lines as MK except during summer)
IASW (original version)
Tiki Room (original version)
Autopia vs. TIS (actually has scenery and stuff to look at, you even go off roading)
Buzz (removable guns make for easier aiming)
Space (completely dark, and smoother with music)
ToT (different scenes, no 4th dimension room)