Do you mean going when it opens without the big production, or do you mean going for Mickey's ToonTown Morning Madness?
We went at opening in December, and it was fine. But I do not know if MTTMM had happened that day. There's no fanfare on a normal day.
If you're talking about MTTMM, when it opens at the same time as DL opens, then my answer is...if you have the vouchers, go. If you don't have the vouchers, having done it and having even been part of the "honorary family" (which really means nothing, LOL), even I can't recommend going to extraordinary measures to get a voucher.
If you're asking about MTTMM, know that they delay its start so that people can get back there. You're not missing it while walking from the gates, because everyone is walking from the gates!
They have a little parade to get the performers (not many) and some characters to the little stage area in the food court, then they have a song and dance number. Then the deputy mayor does a little speech (you can see parts of this looking on disneyland.com and searching with the term "madness"), the family of the day is announced (they have chosen that family while waiting for "everyone" to show up...DS was chosen when running up the hill (oops, running) with his pirate hat and sword on, then stopping in his tracks and calling out to "MICKEY!!!" ), then everyone runs to Mickey's house. Oh wait, that last bit might have been b/c the skies opened and it started pouring at that point.
On a regular day, they don't do anything. You just go in and head to Roger Rabbit, or Mickey's house...there have been characters wandering or popping out or at the front of lines of people... Mickey's house changes...when we went in for MTTMM, there were characters all the way through the house, BUT remember it was pouring rain. When we went on a normal day *before* MTTMM Goofy was outside, along with a couple others over the course of an hour or two. When we went in December, we saw Minnie outside, Goofy, Pluto...and only Mickey was in his house.
Hope I've thrown a helpful answer in there somewhere!