My only problem is the size. You've made it quite small in comparison to my mental image of a vast city-sized ship that one could easily get lost in. At the very least I'd think 2 or 3x the size. You could also do a lot more with the look of the default shell than a plain box. Give it a bit of that Timelordiness the rest of it exudes. Otherwise I love it, and it has been a pleasure to watch it evolve. Huge improvements all around.
I do agree that the TARDIS seems that it should be "bigger-er" on the inside. However, I must disagree about the exterior. The "plain box" is what the TARDIS is theorized to look like without the chameleon circuit active. Reference is The War Games
. You can see a row of SIDRAT
s or TARDISs (not sure which one they are) in this clip
from that serial. They're in the rear of the first shot of the clip when Jamie and Zoe are talking to the time lord. Jamie and Zoe also enter one at around 3 minutes into the clip. Here's a picture of a SIDRAT from that serial: