Looks like a great space to work with! Lots of points jump out at me though...
Do you need 4 separate sitting areas? The main room looks pretty crowded - I'd make one bigger sitting area in the open plan space, and not sure what you'd do with an upstairs space like that? Maybe make that the cinema/gaming area and have the downstairs room as a snug.
Is there a 'back door' somewhere? I assume some of the glass in the big open plan space is sliding/bifold doors, but I'd have a door from the utility too, so you're not traipsing out through the living areas when you're gardening/hanging washing out etc. I'd make the utility a bit bigger too. Also think about the noise from a full spinning washing machine next to your TV room/snug. I wouldn't necessarily move it, but put good insulation in that wall.
The kitchen looks a bit pared back for a house of that size. Looks like plenty of storage (I assume the cupboard area is a walk-in pantry type thing), but where are you going to put 'stuff'? Some kind of dresser/sideboard next to the kitchen maybe, but the focus seems to be on living-room style furniture.
Have you thoughts about having a focal point, like a fireplace, downstairs? Can really make a difference.
If you're going to have a home cinema room (I assume that's the Theatre room), make sure you can lay it out so the seats face the screen - currently everyone is either looking left or right to see the TV.
Living in a house with an internal garage, I resent how much floor space it takes up. Do you really plan to park 2 cars in there? I'd use the space for people rather than cars.
Why is the downstairs bigger than upstairs? If you're building from scratch, why not use the full footprint? Either with an amazing double height element somewhere, or with a balcony from a bedroom (depends on your outlook of course!).
If I was building/designing from scratch, I would 100% build some 'hobby' space into it. We are lucky to have spare bedrooms, so I have an office/sewing room, and DH has an office/guitar room. Ideally I'd separate them and have a tiny corner for an office somewhere and then space to enjoy for hobbies.
That's more than I originally intended, but new things kept occurring to me! I assume an architect designed it? It feels a bit unambitious and lacking in creativity - more what I'd expect to see from a house builder building an estate, rather than someone designing a one-off home. Don't get me wrong - it's a great space, and you could certainly live in it as is with no major issues, but it feels like you could do a lot more with it.