I thought St. Denis was great, so I'm going to try and put some impressions down before they get lost or mingled with others I'll be seeing. The abbot of St Denis abbey wanted to bring in some 'modern' design to his new Abbey church; he wanted light which would express the light of God's creation. He also wanted it to soar to the heavens lifting man's spirit.
To do this he needed to make the walls taller and with great expanses of stationed glass. Previously, Romanesque architecture needed massive walls to hold up the weight of the vaulted ceilings, but with the new style, walls would be supported by flying buttresses, allowing the walls to open up into window space. He succeeded wonderfully. Three main innovations made this work: the flying buttress, the pointed arch, and the vaulted ceiling. We see all three at St Denis.
Some impressions: the clorestory windows (the very highest level) go completely around the basilica, except for the west end where there's a great organ. He also has the triforium (the middle) level full of stained glass! The nave aisles seem very wide, but then this is my first. The apse has double aisles. The inner columns of the pillars go from floor to ceiling, lifting ones eyes to God .
And of course, this basilica is famous as a Royal Necropolis - a burial place for Kings and their families. There are a lot of tombs there, and fancy carved monuments. Quite interesting.