The church is beautiful and the town of Milan too. Most of the guidebooks says Milan is nothing special, but i enjoyed the 2 days there much (one more day would be better). There are many places which are worth to see.
As mentioned below - it is quite difficult to see The Last supper, because of the plenty of tourists who want to see it. For the last moment travellers i can mention www.zaniviaggi.it who has tickets - of course for a higher price as part of a guided tour. This is the way how i got in and i can recommend the tour.
The church is very nice, i enjoyed the stay inside as there was a mass and it was quite magical. The painting itself is not in church but in refectory and in the same room is another master piece - Crucifixation.
I hope i will have a chance to get to Milan once again