Heck, just seeing Mickey and Donald on the same screen as Bugs and Daffy is a Real Life CMOA in its own right.
Also the fact that the sign-offs of Porkie Pig and Tinkerbell are blended together flawless in the end.
Even if it didn't work out, Roger barging into the Acme warehouse with a gun to try and save Eddie and Jessica from Doom's clutches is pretty impressive. Considering he knew full well that Doom wanted to kill him, that took guts.
Doom gets one of his own:
Doom: The rabbit says one way or another he and his wife gonna be happy. Is that true? Eddie: Pal, what do I look like? A stenographer? Lt. Santino: Shut your yap, Eddie. The man's a judge. Doom: That's alright, Lieutenant. From the smell of him, I'd say it was the booze talking. (Eddie glares at him)
Eddie manages to get back at him good though with the good ol' handbuzzer.
META: Bob Hoskins deserves some major props for his phenomenal acting. He's TALKING TO AIR for about 95% of the time, but you honestly believe that the cartoons are there with him. A crowning example is Eddie walking through the Maroon Cartoons lot, pausing to observe all of the cartoon antics going on around him. None of which is actually thereand you can't tell.
Judge Doom deserves a mention too. He is probably the only villain who can pull off a high pitched squeaky voice and make it sound legitimately threatening.
If you know anything about the legal nightmare of Disney and WB allowing their characters to be used in the film, it's a clear miracle that the movie was made at all. In particular, the two companies' properties had to share exactly the same amount of screentime, which is so smoothly integrated that you'd never notice unless you're looking for it.
Another star of the movie is simply the Visual Effects of Awesome. Never before has animation been so convincingly and brilliantly fused with live-action footage (with no computers, mind you) making cartoons actually look like they physically occupy space in reality. It really set the bar for Live-Action/Animation hybrid films even today.
The filming of the car chase alone deserves mention. It was filmed with Bob Hoskins inside of a custom built vehicle resembling a go-kart. The wheel Bob had was made of rubber and bendable to make it cartoony, while the kart itself was driven by a second driver sitting below him and close to the road; all of which was drawn over later. For certain shots Bob was replaced by a drawn counterpart, but they go by so fast you would never know unless you freeze frame them (Such as when they're in the alley and Roger spins the car the other way)