Micheal is right on the button with the first version Summilux. It is NOT a very impressive lens by todays standards. It was a bit of a desperate gamble by Leica in the late 50's to have something to fight off the Nikon 35f1.8. The Summilux 35f1.4 with a # over 2.000 000 is one to go for. For one reason, the hood is less than $300 and stays on (the first version 35f1.4 had a hood than was very prone to falling off and getting lost). The later version has a clip-on hood that it shares with the Summicron 35.
Unfortunately, the Summilux 35f1,4 from the 60's,70's and 80's is a highly priced collectible and priced accordingly. It is a nice lens, but not at the prices they ask for it!
Today we have alternatives that are a/better or equal to it and b/much more reasonably priced.
Voigtlanders 35f2.5 and Nokton 35f1.4 (which was designed and produced as an improved version of the pre-Asph Summilux, Better flare control and sharper at f1.4 but otherwise very much like the old Summilux) . The Zeiss Biogon 35mm f2/0 (I call it "the Summicron killer"). Kind of big, but very.very good.
If you like shooting at ragged edge in low light, there is the 35f1.2 VC - cutting edge quality in a largish package. Unique lens!
You also have the Hexanon 35f2's - my favourite is the small UC version in screw-mount. Nice qualiity but a bit of a collectible and hence difficult to find.
What is amazing is that if your heart so desires, you can get the 35f1.2 VC, the Zeiss 35f2 Biogon and the 35f2.5 VC or the 35f1.4 Nokton for less than a used 35f2 Asph Summicron!!!!