I haven't yet played Maniac Mansion. Although Maniac Mansion is completely playable inside Day of the Tentacle itself.
Maniac Mansion puzzles are a bit easier than DOTT. MM was one of my favorite games on the nes, I was a bit disappointed when I played MM through DOTT because on the nes version all the kids had a background song that played whenever you played as them, but through DOTT there is no music playing on MM when you play through the game. The music was great on the nes so I did miss it, but at least the graphics were quite a bit better.