It's obvious that for most of classic-Who, with all this 'High Gallifreyan' lark, they were just making it up as they went along, scrawling any old vaguely arabic-looking nonsense on the side of Rassilon's Tomb or in the Doctor's diary, but with Nu-Who they clearly got their act together and came up with the lovely circular script we see today:
A plain old bog-standard linear script is locked into time itself, everlasting but not eternal; running giddily from then to now and bubbling on ahead of itself, pregnant with possibility and fecund with the future. It's just like this post, this blog, this life.... dribbling on without end or goal in sight. Always a reference section, always an epilogue, a sequel, a counter-argument, a Phantom Menace, always more ....
But a circular script?... that's like God... It's a stroke of genius. A circular script is literally going nowhere: beautiful, eternal, whole, without beginning or end.
Linear script is fine for science or philosophy, or any open-ended quest for the future, but circular says complete, finished, sorted, done. It is all at once; outside of the then and now and the day and tomorrow.
There's an aesthetic to it as well: It floats above the world, even the merest additional footnote would mar it's circular perfection. It can't be extended - you can only elaborate upon it within the confines of it's own circularity.
But that's means that really it's a dead language isn't it? A closed, ossified script, redolent of a civilisation that has reached its peak, locked into its own never-ending circularity. Circular scripts are, in the end, only good for elaborate pretty patterns or spells or poems or jokes - and that fits the Time Lords pretty well I think .
I hope they only bring them back for a little bit. They're like the Jedi, not as interesting as you think they'll be... best kept to the shadows with their pretty, little spinning laws of time......