If you're someone who truly enjoys cocktails and gastronomy then I would put Barchef on your to-try list.
Barchef isn't a lounge or a bar in my opinion. It's an experience.
Don't go for regular cocktails get something unique off the menu or even have a bartender make you something off-the-cuff. The cocktails are so unique and fun to enjoy. Yes they are pricey but you sip them a lot longer than you would a regular cocktail and you'd probably only order one or two for the evening.
The Smokey Manhattan is probably the show stopper of the menu. It's a beautifully crafted Manhattan carried in a smoking vessel to be infused with all the wonderful tones and flavours of the smoke.
The space itself can be more loungy in my opinion. If you're not sitting at the bar your basically missing most of the action.