well you've probably heard this before, but my first piece of advice is:
Don't compare
Disneyland Paris to any of the other Disney Parks. Go open-minded and enjoy the experience!
My must-do's:
- Space Mountain: you
shouldn't miss this, it's completely different to the U.S. versions and it has loops
- Pirates of the Caribbean: I'm mentioning this because it hasn't been upgraded with the movie characters yet, which makes it worth riding it, if you miss the old ride. The same goes for IASW, and Star Tours (though the latter is screaming for a rehab)
- Phantom Manor: From what I remember from WDW and DL it has a different storyline, this one is linked to the town and the mine from BTM stories and it's darker, scarier than the U.S. versions
- Sleeping Beauty Castle: Please don't forget to go up to the first floor and see the murals and vitraux. Also, pay a visit to the dragon underground, you won't find him back home.
-Once Upon a Dream Parade: Nice daytime parade ;D
What would be must-do's at WDW would be must-do's here, but I would skip Peter Pan's Flight, Snowhite, the teacups, etc. Anything that can be quite similar can ve avoided so you can focus on the things that are unique to this park... or other activities such as taking pictures
Do BTM first thing in the morning EMH if you're going on high season or leave it for last thing in the evening. It gets insanely crowded
I can't recommend fireworks because I don't think there are any fireworks show in May.
For the Studios:
Crush's Coaster: I don't think it exists in the american parks. But again, do this first thing in the morning ...i'd even say, RUN to the attraction as soon ASAP before the lines get too long (usually high season). Oh, and remember that this park closes earlier than Disneyland Park.
Cinemagique
Tower of Terror
Rock n'Roller Coaster
Motors...Action! Because I think I read somewhere that this was originally from DLRP so it's interesting to watch
Backlot tour let me down last year so I won't mention it, unless you need to rest your feet for a while.
I haven't been to the Toy Story new section yet, so I don't know if there's anything that I would recommend from there for adults
As for restaurants, Walt's at Disneyland Park, Restaurant des Stars at Disney Studios and (for me) Chef Mickey, Annette's, Rainforest Cafe or Planet Hollywood at Disney Village
Oh and for me, a must-do is always a hot dog with cheddar cheese at Casey's Corner. I'm not at disney if I don't have one of those.
I'm sure there are lots of other things to recommend but I can't think of anything else right now.