The roof top deck (when open during the summer months) rocks. I live in the area and have visited several times. The upstairs service staff have always been attentive and courteous and the music is great. The waitresses seem to remember me and my favorite order - which is a pint of village and the nachos.
Speaking of which, I'm going to step out on a limb here and make a rather bold statement... the nachos at Molly's are arguably the best I've had in Calgary. I know, who would think that an Irish Pub would make great nachos? The chips and adornments are brought to the table smoking hot and there is always a side tray with three bowls (one for freshly chopped tomatoes, guacamole and cold sour cream).
The only reason that I can't give Molly's a solid 5 is that the downstairs is somewhat of a dungeon and although the service is decent, it almost appears that I'm in two different restaurants from a customer service perspective (the service is better upstairs).
The roof-top at Molly's is definitely a fun place to meet up with friends for a pint or two.